Physics report
on this topic:
“Magnetic recording.
Magnetic storage media”
The technology of recording information on magnetic media appeared relatively recently - approximately in the middle of the 20th century (40s - 50s). But already a few decades later - the 60s - 70s - this technology has become very widespread throughout the world.
A very long time ago, the first gram-disc was born. Which was used as a carrier of various sound data - various musical melodies, human speech, songs were recorded on it.
The recording technology itself was quite simple. With the help of a special apparatus in a special soft material, vinyl, serifs, pits, stripes were made. And from this a record was obtained, which could be listened to with the help of a special apparatus - a patiphone or a player. The patifon consisted of: a mechanism that rotates the plate around its axis, a needle and a tube.
A mechanism was activated that rotated the plate, and a needle was placed on the plate. The needle floated smoothly along the grooves cut in the plate, making different sounds at the same time - depending on the depth of the groove, its width, inclination, etc., using the phenomenon of resonance. And then the pipe, located near the needle itself, amplified the sound “carved out” by the needle. (Fig. 1)
Almost the same system is used in modern (and used before too) magnetic recording readers. The functions of the constituent parts remained the same, only the constituent parts themselves have changed - instead of vinyl records, tapes with a layer of magnetic particles deposited on top of them are now used; and instead of a needle - a special reader. And the tube that amplifies the sound disappeared completely, and in its place came speakers using the already bolder new technology for reproducing and amplifying sound vibrations. And in some industries that use magnetic media (for example, in computers), the need to use such tubes has disappeared.
A magnetic tape consists of a strip of a dense substance onto which a layer of ferromagnets is deposited. It is on this layer that information is “remembered”.
The recording process is also similar to the process of recording on vinyl records - using a magnetic induction instead of a special apparatus.
A current is applied to the head, which drives the magnet. The recording of sound on a film occurs due to the action of an electromagnet on the film. The magnetic field of the magnet changes in time with sound vibrations, and due to this, small magnetic particles (domains) begin to change their location on the surface of the film in a certain order, depending on the effect of the magnetic field created by the electromagnet on them.
And when playing the recording, the reverse recording process is observed: the magnetized tape excites electrical signals in the magnetic head, which, after amplification, go further to the speaker. (Fig. 2)
Data used in computer technology is recorded on magnetic media in the same way, with the difference that data requires less space on tape than sound. It's just that all information written to magnetic media in computers is written in a binary system - if, when reading from a media, the head “feels” that the domain is under it, then this means that the value of this piece of data is “1”, if not “feels”, then the value is “0”. And then the computer system converts the data recorded in the binary system into a system that is more understandable to humans.
There are many different types of magnetic media in the world today: floppy disks for computers, audio and video cassettes, reel tapes, hard disks inside computers, etc.
But new laws of physics are gradually opening up, and with them new possibilities for recording information. Already several decades ago, a lot of information carriers appeared, based on a new technology - reading information using lenses and a laser beam. But all the same, magnetic recording technology will exist for quite a long time because of its ease of use.
Abstract plan
1. Magnetic media………………………………………………….……3
1.1 Floppy disks……………………………………………………….….4
2. Optical media……………………………………………….…...5
2.1 DVD……………………………………………………………………..5
2.2 Divx………………………………………………………………….…..6
2.3 FMD ROM - drives of the third millennium………….……...6
2.3.1 Operating principles of FMD ROM…………….….…6
2.4 Blu-Ray technology - successor to DVD………………………….…..7
2.4.1 Specifications of Blu-ray Disc……………………………..….….8
3. Magneto-optical carrier……………………………………….….8
3.1 Size 5.25’’…………………..…………………………………..…..9
3.2 Size 3.5’’……………………………..………………………….….9
3.3 Non-standard devices……………………………………….…..9
3.4 Advantages of MO disks…………………………………………..9
3.5 Disadvantages of MO disks………………………………………………….9
4. Mobile media………………………………………………………10
4.1 USB Flash Memory ...………………………………………………....10
4.2 Operating principle...……………..………………………………....10
4.2.1 NOR……………………………………………………………..10
4.2.2 NAND…………………………………………………………...11
4.3 Features……………………………………………………...11
4.4 File systems………………………………………………………………11
4.5 Application………………………………………………………….11
4.6 Types of memory cards………………………………………………………12
1. Magnetic media
The technology of recording information on magnetic media appeared at the beginning of the 20th century, but already in the 60s and 70s it spread throughout the world.
Melodies, human speech were recorded on the first gramophone record.
The recording technology was simple: serifs, pits, grooves were made in soft material - vinyl. It turned out a record, which was listened to with the help of another device - a gramophone or a player. The gramophone consisted of a mechanism that rotated the plate around its axis, a needle and a tube.
The needle floated along the grooves, making sounds according to the principle of resonance - depending on the depth of the groove, its width, inclination, etc. The tube, located near the needle itself, amplified the sound (Fig. 1).
A similar system is used in magnetic recording readers. The functions of the components remain the same, the components themselves have changed - instead of vinyl records, tapes are used with a layer of ferromagnets deposited on them, on which information is “remembered”. Instead of a needle - a reader. Instead of a tube that amplifies the sound - speakers.
Recording is carried out using a magnetic induction head, a current is applied to it, which activates the magnet. The magnetic field changes in time with sound vibrations, and magnetic particles (domains) change their location on the film surface in accordance with the electromagnet field.
During playback, the reverse process occurs: the magnetized tape excites electrical signals in the magnetic head, which, after amplification, enter the speaker. (Fig. 2)
In computer technology, data is recorded on magnetic media in the same way, but they require less space on the film. Information in computers is written in a binary system: if, when reading, the head “feels” the domain below it, then the value of this particle is “1”, if it does not “feel”, then it is “0”. The computer converts this data into a human-understandable system.
There are many types of magnetic media: floppy disks, audio and video cassettes, reel-to-reel tapes, hard disks inside computers. For example:
Barracuda 180 hard drive
Disk transfer rate: up to 48 MB/s
Spindle speed: 7200 rpm
Interface: Ultra160 up to 160 MB/s, FibreChannel up to 200 MB/s
Tensile strength 150 G in non-working condition
Noise level: 37 dB
Search time: 7.5ms
Very capacious internal hard drive for PC.
Hard drive Cheetah X15_36
Capacity: 36.7 and 18.3 GB
Disk transfer rate: up to 48.9 MB/s
Spindle speed: 15.000 rpm
Interface: Ultra320 up to 320 MB/s
Ultimate tensile strength G in non-working condition
Noise level: 35/37 dB
Search time: 3.9ms
The fastest hard drive for PC.
1.1 Floppy disks
The floppy disk drive (Floppy Disk - FD - floppy disk, or floppy disk) has two motors: one ensures a stable disk rotation speed, and the second moves the write-read heads. The speed of rotation of the first motor depends on the type of diskette and ranges from 300 to 360 rpm. The motor for moving the heads in these drives is always stepper. With its help, the heads move along the radius from the edge of the disk to its center in discrete intervals. Unlike a hard drive, the heads in this device do not “hover” above the surface of the floppy disk, but touch it.
For each of the floppy disk sizes (5.25 or 3.5 inches), there are drives of the corresponding form factor.
Floppy disks of each size are double-sided (Double Sided, DS), single-sided are outdated. Recording density can be: single (Single Density, SD), double (Double Density, DD, capacity 360 or 720 KB) and high (High Density, HD, capacity 1.2, 1.44 or 2.88 MB). The density is determined by the size of the gap between the disk and the magnetic head, and the quality of recording and reading depends on the stability of the gap. To increase the density, the gap is reduced, but the requirements for the working surface of the discs are increased.
Material for the manufacture of magnetic disks - aluminum alloy D16MP (MP - magnetic memory). It is non-magnetic, soft, strong enough, well processed.
Floppy disk devices consist of a read/write device - a floppy drive and a direct medium - a floppy disk.
A floppy disk is a layer of soft magnetic material deposited on a polymer non-magnetic plastic substrate. The media is placed in a paper or plastic housing. The coating is applied on both sides of the floppy and read/write is done on both sides. Floppy disks of different diameters have different case designs. Floppy disks with a diameter of 5.25 inches are placed in a paper casing, and 3.14 in a plastic one. The floppy disk in the shroud is freely rotated by the floppy drive through the center grip window, which allows the track to pass under the read/write head.
There are holes on the floppy casing: central grip (3), head positioning hole (1), physical write protection hole (5, 8), guide holes and grooves (2), hole for determining the full rotation of the media (4). The hole for positioning the magnetic read/write heads of 3.14-inch media is closed with a metal latch (7), and the hole for central grip and rotation on the drive spindle, unlike the 5.25-inch media, is located only on the underside of the floppy disk. Each floppy disk must be prepared to receive data - formatted. Floppy disks are formatted using disk formatting programs.
The floppy disk indicates a parameter called the number of dots per inch of the media - Track per inch (TPI). TPI shows the maximum density of placement of regions of independent magnetization of the carrier. In accordance with the characteristics, the disk is formatted within its capabilities, otherwise data may be lost after the write operation.
A floppy drive is a device that reads/writes from/to a floppy disk. Each type of diskette requires its own device. But there are also mixed drives that combine devices for reading 3.14 and 5.25 inch floppy disks. Drives are located inside the system unit. However, external versions are also available. Outside the system unit is the front panel of the drive, on which the control elements are located - the button for fixing / ejecting the floppy disk, the hole for inserting / ejecting the diskette, the device access indicator. Inside the drive consists of: motor; carrier rotation control systems; read/write head positioning control systems; circuits for generating and converting signals, and other electronic devices. Drives are connected to computer circuits with an interface cable - a cable. At the ends and / or along the length of the cable there are connectors, one of which is used to connect the cable to the drive; the other is with the disk device interface on the motherboard. The power cable connects the drive to the supply voltage.
Reading / writing information to a floppy disk gives low exchange rates, the amount of information is up to 2 megabytes. Therefore, floppy disks are used as a means of transportation and archival storage of small amounts of information. The reliability of diskettes is low. They are subject to the harmful effects of temperature, hydrometric, magnetic, mechanical and other factors. Therefore, diskettes should be handled with care.
Unacceptable: storage of floppy disks in places exposed to magnetic fields, moisture, mechanical stress, copious amounts of dust, sudden changes in temperature. Carefully insert and remove a floppy disk from the drive only after the disk access indicator has turned off. It is necessary to clean the read/write heads with a cleaning disk and cleaner. Media life varies depending on usage and original quality. High-quality floppy disks withstand up to 70 million head passes along the track, which corresponds to a period of intensive use of up to 20 years. Poor quality floppy disks are prone to shedding particles of magnetic coating and demagnetization.
2. Optical media.
In a CD or DVD, a reflective aluminum layer is applied to an extruded polymer substrate, which makes them opaque. When reading, a semiconductor laser beam is reflected from the layer with the recorded information. The reflected beam is fixed by a detector-receiver. Those. reading goes according to the principle: the beam hit or did not hit the receiver. The maximum specific capacity of the disk is determined by the size of the light spot from the laser, which depends on the wavelength (for red lasers - 650nm). You can use two layers, and make one of the layers transparent to radiation with a certain wavelength, as implemented in DVD.
The DVD standard is based on the principles:
- · large capacity and the possibility of its further growth;
- · backwards compatible with existing CDs;
- · compatibility with future recordable DVDs;
- · single file system for all applications;
- · single interactive standard for computer and television;
- · reliability of data storage and their subsequent reading;
- · high performance when writing and reading data for sequential and random access to data;
- · lack of auxiliary structures such as cartridges and caddies;
- · affordable price.
Externally, the design of a DVD is similar to that of a CD - with the same geometric dimensions (diameter - 120 mm, thickness - 1.2 mm), but it is much more complicated. To increase the amount of data while maintaining the same geometric dimensions of the disk as the CD, the following steps were taken:
- · reduction in the size of depressions (pits) on DVD to 0.4 microns;
- · reducing the distance between adjacent tracks (tracks) to 0.74 microns;
- · placement of information-carrying layers on several floors (up to 8 pairs, and this is not the limit).
DVD can be either single sided or double sided. Structurally, a double-sided disc consists of two discs 0.6 mm thick glued together with non-working surfaces. The DVD standard specifications provide for four types of discs with different information capacities:
- · single-sided single-layer disc (4.7 GB, video resource - 133 min.);
- · single-sided double-layer disc (8.5 GB, video resource - 240 min.);
- · double-sided single-layer disc (9.4 GB, video resource - 266 min.);
- · double-sided dual-layer disc (17 GB, video resource - 481 min.).
The capacity of a single-sided single layer disc is seven times and a double-sided double layer disc is twenty-six times the capacity of a standard CD.
For reading DVDs, a red spectrum beam is used with the possibility of double focusing at a wavelength of 650 nm or 635 nm, depending on the thickness of the disc being read. The DVD drive itself detects what type of disc is being used and automatically rotates the lens to the correct beam focusing position.
A DVD, like a CD, is insensitive to dust, scratches, and finger touches.
2.2 Divx
Digital Video Express has developed a new Divx disc format for burning movies once. Divx is the name of the system installed directly in the player, which allows consumers to enjoy the right to rent a video film for two days, regardless of the date of purchase of the disc. The development of this format is connected with the organization of a temporary video rental system: having bought a disc, you do not have to return it back. It can only be played on Divx players. Large companies such as Disney, Dream-Works, Paramount, Universal announced their support for this format. This disc is not compatible with DVD players. Divx enforces write breaking on the disc.
2.3 FMD ROM - drives of the third millennium
Superiority of FMD ROM over DVD:
Size/capacity ratio. Prototype FMD ROMs are capable of holding up to 140 GB with a disk size of 12 cm in diameter, i.e. on 5 inch media. This is ten layers. The number of layers will increase. This will make it possible to create disks with a capacity of tens of terabytes. At the moment, such a volume of information is provided by the use of disk arrays that occupy entire cabinets and rooms.
New volumes will also require appropriate access speeds.
FMD ROM is a polymer matrix with a photochromic substance, at a cost it is a plastic disk. There is no cost of creating expensive translucent layers like in DVD. Actually, there are no layers in the usual sense of the word.
2.3.1 Principles of operation of FMD ROM.
FMD ROM is a transparent disc in CD or DVD format. The FMD ROM disk is monolithic and at the same time is divided vertically into conditional "layers" (layer). They are not layers in the usual sense, this is a disk formatting parameter similar to the sector and track of magnetic media. The thickness of these layers is strictly fixed.
Two layers in a CD or DVD is the limit, it's hard to do more because you need precise focusing systems that will only work in a lab. Mass production of such systems is expensive and unprofitable.
The FMD developers proposed a solution: the material containing the recorded information does not reflect, like the substrate in a DVD or CD, but radiates! The phenomenon of fluorescence is used, that is, when illuminated with activating radiation (in this case, a semiconductor laser with a certain wavelength), the substance begins to radiate, shifting the spectrum of the radiation incident on it towards red by a certain amount. Moreover, the magnitude of the shift depends on the thickness of the layer. By choosing such a layer thickness that the reflected light spectrum is shifted relative to the wavelength of the emitting laser by a strictly defined value, for example, by 30 or 50 nm, it is possible to record information deep into the disk with high reliability and subsequently read it without data loss.
The proposed name for FMD ROM is "3D disc".
The recording density will depend on the sensitivity of the recording detector. The smaller the additional radiation of the fluorescent substance, added to the frequency of the working laser, which can be fixed, the greater the number of layers can be accommodated in one disk.
The emitted light from the fluorescent layer is incoherent and contrasts well with the reflected laser light, which is an additional guarantee of reading reliability. Reflections will occur from the disc surface and other recorded layers. The signal degradation in conventional disks increases with the number of layers. In the case of fluorescent discs, this degradation occurs much more slowly. FMD ROM, even with more than a hundred layers, there will be no strong distortion of the useful signal. Using a blue laser (480nm) it is possible to increase the recording density up to tens of terabytes per FM disc. It is possible to create a disk with 1000 layers - these are already submolecular sizes. Theoretically, it is possible to create a spot several molecules in size, the only problem is how to fix such a small radiation.
One of the main features of this development is the possibility of parallel reading of layers (ie, the sequence of bits will be written not by "tracks", but by layers) - the data sampling rate in this case should be very high.
The photo shows a prototype drive for such disks.
The principle of recording on FMD ROM is based on the phenomenon of photochromism. Photochromism is the property of some substances under the action of activating radiation to reversibly change from one state to another, while changing their physical properties (for example, such as color, the appearance / disappearance of fluorescence, etc.). The material that makes up the FMD ROM contains a special photochromic substance, which is cyclized under the influence of a laser beam of a certain wavelength, turning into the necessary stable fluorescent. The reverse recyclization reaction, leading to the disappearance of fluorescent properties (erasing operation), occurs under the action of a laser with a different wavelength. The erasing frequency of the laser is chosen so that it does not occur in everyday life, in order to avoid data loss. The reading laser should never make changes to the data stored on the disk.
The idea of using photochromes as information carriers is not new. She is about thirty years old, but only now she is put into practice.
2.4 Blu-ray technology - successor to DVD
Blu-ray Disc, BD (English blue ray - blue beam and disc - disc; spelling blu instead of blue - intentional) is an optical media format used for high-density recording and storage of digital data, including high-definition video. The Blu-ray standard was developed by the BDA consortium. The first prototype of the new carrier was presented in October 2000. The modern version is presented at the international exhibition of consumer electronics Consumer Electronics Show (CES). The commercial launch of the Blu-ray format took place in the spring of 2006.
Blu-ray (lit. "blue beam") gets its name from the use of a short wavelength (405 nm) "blue" laser. The letter "e" was dropped from the word "blue" to register a trademark.
From 2006 until 2008, Blu-ray had a serious competitor - the alternative HD DVD format. Within two years, many of the major film studios that originally supported HD DVD gradually switched to Blu-ray. Warner Brothers, the last company to release in both formats, phased out HD DVD in January 2008. On February 19, 2008, Toshiba, the creator of the format, stopped developing HD DVD.
BlueLaserDVDdisk
A single layer Blu-ray disc (BD) can store 23.3/25/27 or 33GB, a dual layer disc can store 46.6/50/54 or 66GB. Also in development are 100 GB and 200 GB discs using four and eight layers, respectively. TDK has already announced a 100 GB four-layer disc prototype.
On October 5, 2009, the Japanese corporation TDK announced the creation of a recordable Blu-ray disc with a capacity of 320 gigabytes. The new ten-layer media is fully compatible with existing drives, according to TechOn.
BD-R (Recordable) and BD-RE (Recordable) discs are currently available, and the BD-ROM format is under development. In addition to the standard 120mm discs, 80mm discs have been released for use in digital cameras and camcorders. The planned volume is 15 GB.
Write Drive Blu-ray discs
For compatibility with CD and DVD, Blu-Ray, the drive has two lasers - the main blue and the additional red. Compatibility with previous formats is needed, because. the DVD and CD library is very large and the consumer will not want to give it up.
Drive writingblu-raydiscs Head with laser
2.4.1 Features of Blu-ray Disc
| Media capacity | 23.3 GB / 25 GB / 27 GB / 50 GB / 100 GB |
| Laser wavelength | 405nm (blue-violet laser) |
| Lens pitch | 0.85NA (numerical aperture) |
| Transfer rate | |
| Disc diameter | |
| Disc thickness | 1.2mm (optically active layer thickness - 0.1mm) |
| Track thickness | |
| Minimum point length | 0.160/0.149/0.138um |
| Recording Density | 16.8/18.0/19.5Gbit/inch2 |
| Video recording format | MPEG2 video (for video player), |
| Audio recording format The MO disk is a 1.2 mm thick polycarbonate substrate on which several thin film layers are deposited. This is the magnetic part of the technology, and the optical part is represented by a reading laser. The protective layer protects the disc surface from damage. Reflective - necessary for the laser to work. Dielectric layers perform two functions: 1) thermally insulate the magnetic layer for efficient use of laser energy during recording; 2) increase the effect of polarization when reading. The MO disk itself is placed in a plastic box with a shutter and a write protection window. Recording on a magneto-optical disk is carried out as follows: laser radiation heats up a section of the track above the Curie point temperature, after which an electromagnetic pulse changes the magnetization, creating prints equivalent to Petes on optical disks. Reading is carried out by the same laser, but at a lower power, insufficient to heat up the disk: a polarized laser beam passes through the disk material, is reflected from the substrate, passes through the optical system and hits the sensor. In this case, depending on the magnetization, the polarization plane of the laser beam changes, which is determined by the sensor. 3.1 Size 5.25'' The maximum capacity is 9.1 GB. DVDs are inferior to magneto-optics not only in terms of speed, but also in terms of data storage reliability. MO disks withstand a huge number of rewriting cycles, are not sensitive to external magnetic fields and radiation, and guarantee the safety of recorded information for fifty years. Recording is done using two heads. Optical provides heating, and magnetic changes the direction of the magnetic field. Both sides of the disc are written at the same time, so the speed of writing and reading data is doubled. 3.2 Size 3.5'' 3.5 format magneto-optics, unlike 5.25 format magneto-optics, is aimed at the mass market. Advantages: compactness, high speed and reliability. The GigaMO high density recording format is 1.3GB and 2.3GB. These formats provide full backward compatibility of devices with media of previous generations (128-640 MB). 3.3 Non-standard devices A disk with a diameter of 50 mm (slightly less than 3.5 inches) will hold 730 MB. It is ideal for use in handheld and digital devices for various purposes. Disc diameter 50.8mm, high density. The volume of stored information is approximately equal to 1-2 GB, intended for use in portable computing devices, mainly laptops. 3.4 Benefits of MO disks ¨ Low susceptibility to mechanical damage ¨ Weak exposure to magnetic fields ¨ Guaranteed recording quality ¨ Works like a hard drive ¨ [edit] 3.5 Disadvantages of MO disks ¨ High power consumption. To heat up the surface, lasers of significant power are required, and, consequently, high energy consumption. This makes it difficult to use MO recorders in mobile devices. ¨ The high price of both the disks themselves and the drives. ¨ Low prevalence. 4 Mobile media 4.1 USBFlash Memory Flash memory (eng. Flash-Memory) - a kind of solid-state semiconductor non-volatile rewritable memory (PEPROM). It can be read any number of times (within the data storage period, typically 10-100 years), but such memory can only be written to a limited number of times (maximum - about a million cycles). Flash memory is common and can withstand about 100,000 write cycles, much more than a floppy disk or CD-RW can handle. It does not contain moving parts, so, unlike hard drives, it is more reliable and compact. Due to its compactness, low cost and low power consumption, flash memory is widely used in digital portable devices - photo and video cameras, voice recorders, MP3 players, PDAs, mobile phones, as well as smartphones and communicators. In addition, it is used to store firmware. USB flash drives (“flash drive”, USB drive, USB disk) have become widespread, practically replacing floppy disks and CDs. The main disadvantage is the high price/volume ratio, which exceeds this parameter for hard drives by 2-3 times. Work in this direction is underway - the cost of the technological process is getting cheaper, competition is intensifying. In November 2009, OCZ offered a 1TB SSD with 1.5 million write cycles. Another disadvantage of flash memory compared to hard drives is slower speed. Manufacturers of SSD drives claim that the speed of these devices is higher than the speed of hard drives, but in reality it is significantly lower. This leads to a decrease in overall performance. The latest models of SSD drives have already come close to hard drives in this parameter, but they are too expensive. 4.2 How it works Flash memory stores information in an array of floating gate transistors called cells. In traditional single-level cell (SLC) devices, each cell can store only one bit. Some new devices with multi-level cells (eng. multi-level cell, MLC; triple-level cell, TLC) can store more than one bit, using a different level of electrical charge on the floating gate of the transistor. 4.2.1 NOR This type of flash memory is based on a NOR element, because in a floating gate transistor, a low gate voltage indicates one. |
Drives on magnetic and optical media.
Let's name the reasons for the need for external memory in a computer.
1. The preservation of information for later use or for transmission to other people was of great importance for the development of civilization. Before the advent of computers, people used books, photographs, tape recordings, film, etc. for this purpose. By the end of the 20th century, information flows increased significantly and the appearance of computers contributed to the development and use of information carriers that ensure the possibility of its long-term storage in a compact form.
2. Computer RAM has a number of disadvantages associated with its manufacturing technology. Even today, in the 21st century, it does not have a sufficiently large volume and does not contain huge amounts of information. In addition, the contents of RAM are still lost when the computer is turned off. Therefore, the presence in the computer system of another type of memory - external, made it possible to eliminate these shortcomings. The main function of external memory is the ability to store information for a long time. In addition, external memory has a large amount and is cheaper than RAM. And yet, external memory media provide the transfer of information from one computer to another, which is important in a situation where there are no computer networks.
In this way external (long-term) memory - this is a place for long-term storage of data (programs, calculation results, texts, etc.) that are not currently used in the computer's RAM. External memory, unlike operational memory, is non-volatile, but does not have a direct connection with the processor.
External memory media, in addition, provide data transportation in cases where computers are not networked (local or global).
To work with external memory, you must have drive(a device that provides recording and (or) reading of information) and storage devices - carrier.
The main types of drives:
Floppy disk drives (FPHD);
Hard disk drives (HDD);
Drives CD-ROM, CD-RW, DVD. They correspond to the main types of media:
Flexible magnetic disks (Floppydisk);
Hard magnetic disks (Harddisk):
CD-ROMs, CD-Rs, CD-RWs, DVDs. The main characteristics of drives and media:
Information capacity;
Speed of information exchange;
Reliability of information storage;
Price.
Principle work magnetic remembering devices
Magnetic recording is based on the conversion of digital information (in the form of 0 and 1) into an alternating electric current, which is accompanied by an alternating magnetic field. As a result, the surface of magnetic carriers is divided into non-magnetized areas (0) and magnetized areas (1).
In computers of early generations, the functions of external memory were performed by punched tapes and punched cards, as well as magnetic tapes, which are now used very rarely. Magnetic tapes are a serial access device. Data can only be read or written sequentially, if the order is violated, you have to wait a long time until the tape is rewound to the right place. Magnetic tapes are rather slow devices, although they have a large capacity. Modern devices for working with magnetic tapes - streamers have an increased recording speed, and the capacity of one streamer cassette is measured in hundreds and thousands of megabytes, and the data transfer rate is from 2 to 9 MB per minute.
Flexible disk
A floppy disk drive or a floppy disk is a medium for a small amount of information, which is a flexible disk in a protective shell. Used to transfer data from one computer to another and to distribute software.
Diskette device.
Read/Write Window Shutter
plastic envelope
Drive bushing
Write Lock: Disabled/Enabled B
The disc is inside a plastic envelope that protects it from mechanical damage. In order to read or write data, you must insert a floppy disk into the floppy disk drive, the slot of which is located on the front panel of the system unit. Inside the drive, the read/write shutter automatically opens and it is over this place that the read/write head of the drive is installed. The disk inside the drive rotates at a constant angular speed, which is quite low (a few kilobytes per second, average access time is 250 ms). Information is written to both sides of the disc. Currently, the most common are 3.5-inch floppy disks (1 inch = 2.54 cm) and a capacity of 1.44 MB (this is about 600 pages of text or several dozen graphics). The disc can be write-protected. For this, a safety latch is used.
Diskettes require careful handling. They may be damaged if:
Touch the recording surface;
Write on the floppy disk label with a pencil or ballpoint pen;
Bend a floppy disk;
Overheat the floppy disk (leave it in the sun or near the radiator);
Expose the floppy disk to magnetic fields.
Hard magnetic disk
Since the floppy disk has a small volume, it is mainly used to transfer information from one computer to another. The hard disk is the information warehouse of a computer and is capable of storing huge amounts of information.
A hard disk drive (Eng. HDD - Hard Disk Driver) or a hard drive is the most massive mass storage device in which the information carriers are aluminum plates, both surfaces of which are covered with a layer of magnetic material. Used for permanent storage of programs and data.
The hard drive disks are placed on one axis and, together with the read / write heads and the heads carrying them, are placed in a hermetically sealed metal case. This design made it possible to significantly increase the speed of disk rotation and recording density. Information is recorded on both surfaces of the disks.
Unlike a floppy disk, a hard disk spins continuously. Therefore, its rotation speed can be from 3600 to 10000 rpm, the average data search time is 9 ms, the average data transfer rate is up to 60 MB/sec.
The capacity of hard drives in computers in 2000 was measured in tens of gigabytes. The most common drives with a diameter of 2.2, 2.3, 3.14, 5.25 inches.
In order to preserve information and performance, the hard drive must be protected from shock and sudden changes in spatial orientation during operation.
laser disk
CD-ROM (English)CompactdiskRealOnlyMemory - a read-only memory device based on a compact disk)
A 120 mm (approx. 4.75 inch) CD is made of resin and coated with a metallic film. Information is read from this metal film, which is covered with a polymer that protects data from damage. CD-ROM is a one-sided storage medium.
The principle of digital recording of information on a laser disc differs from the principle of magnetic recording. The encoded information is applied to the disc by a laser beam, which creates microscopic depressions on the surface, separated by flat areas. Digital information is represented by alternating pits (zero coding) and light-reflecting islands (one coding). The information printed on the disc cannot be changed.
Information is read from the disk by registering changes in the intensity of low-power laser radiation reflected from the aluminum layer. The receiver or photosensor determines whether the beam reflected from a smooth surface (thus fixing one), was scattered or absorbed (fixing zero). Scattering or absorption of the beam occurs in places where indentations were made during the recording process. The photo sensor senses the scattered beam, and this information is fed to a microprocessor in the form of electrical signals, which converts these signals into binary data or sound.
The CD-ROM rotates at a variable angular speed to provide a constant linear speed when reading. Thus, reading information from the internal sections of the disk is carried out at a greater number of revolutions than from the outer ones. Therefore, access to data on a CD-ROM is faster than data on floppy disks, but slower than on hard disks (from 150 to 400 ms at rotation speeds up to 4500 rpm). The data transfer rate is at least 150 KB and reaches 1.2 MB/s.
The capacity of CD-ROMs is up to 780 MB, which is why multimedia programs are usually released on them.
CD-ROMs are simple and easy to use, have a low unit cost of data storage, practically do not wear out, cannot be affected by viruses, and it is impossible to accidentally erase information from them.
CD-R (Compact Disk Recorder)
CD-R is a recordable disc with a capacity of 650 MB. On CD-R discs, the reflective layer is made of gold film. Between this layer and the base there is a recording layer made of an organic material that darkens when heated. During the recording process, the laser beam heats up the selected points of the layer, which darken and stop transmitting light to the reflective layer, forming areas similar to depressions. CD-R drives, due to the strong reduction in price, are becoming more widespread.
CD-RW (Compact Disk Rewritable)
More popular are CD-RW drives, which allow you to write and rewrite information. The CD-RW drive allows you to write and read CD-R and CD-RW discs, read CD-ROM discs, that is, it is universal in a certain sense.
The abbreviation DVD stands for DigitalVersatiledisk, i.e. universal digital disk. Having the same dimensions as a conventional CD and a very similar principle of operation, it holds an extremely large amount of information - from 4.7 to 17 GB. Perhaps it is because of the large capacity that it is called universal. True, today the DVD disc is actually used only in two areas: for storing video films (DVD-Video or simply DVD) and extra-large databases (DVD-ROM, DVD-R).
The capacity variation occurs as follows: Unlike CD-ROMs, DVDs are recorded on both sides. Moreover, one or two layers of information can be applied on each side. Thus, single-sided single-layer discs have a capacity of 4.7 GB (they are often called DVD-5, that is, discs with a capacity of about 5 GB), double-sided single-layer discs - 9.4 GB (DVD-10), single-sided double-layer discs - 8.5 GB (DVD-9), and double-sided double-layer - 17 GB (DVD-18). Depending on the amount of data that needs to be stored, the type of DVD disc is selected. When it comes to films, double-sided discs often store two versions of the same picture - one widescreen, the second in the classic television format.
The main parameter of CD-ROM drives is the data reading speed. It is measured in multiples. The unit of measurement is the read speed in the first serial samples, which is 150 KB / s, so a drive with a double read speed provides a performance of 300 KB / s, with a quadruple - 600 KB / s, etc.
In order to preserve information, laser discs must be protected from mechanical damage (scratches), as well as from contamination.
Structure surfaces disks
Formulation of the problem.
Imagine a book shaped like a long ribbon.
Is it convenient to search for the necessary information in such a “book”? Why?
What is the convenience of finding the necessary information in a regular book that has pages? Why?
Conclusion: in the book you can find the information you need without problems, because it has a convenient structure, namely, it is divided into pages. It is inconvenient to search for information in a book made in the form of a long tape, because it is not clear in which part of the tape it is located. Pages have their own numbers, so to find the information you need, it is enough to know the page number on which it is located, i.e. the book has a structure. Without this structure, finding information is difficult.
Since a book is an analogue of external memory, the surface of any disk must also have a certain structure. Just as in the manufacture of a book a large sheet of paper is cut into pages and then assembled together, so the surface of the disk is "cut" into pieces - "pages".
Magnetic disks.
Any magnetic disk is not initially ready for operation. To bring it into working condition, it must be formatted, that is, the disk structure must be created. For a floppy disk, this is magneticconcentric tracks - divided into sectors. And the hard magnetic disk still has cylinders, since the hard disk consists of several plates.
A sector is too small a "piece" of the disk surface (like a line on a page). Therefore, sectors are combined into larger "pieces" - clusters.
The volume of a disk can be calculated as follows.
Volume = number of sides * number of tracks * sectors * sector volume.
The farther from the center of the disc, the longer the tracks. Therefore, with the same number of sectors on each of them, the recording density on the inner tracks should be higher than on the outer ones. The number of sectors, the capacity of the sector, and, consequently, the information volume of the disk depend on the type of drive and formatting mode, as well as on the quality of the disks themselves.
laser discs
Unlike magnetic disks, a CD-ROM has only one physical track in the form of a spiral that goes from the outer diameter of the disk to the inner one.
Example 1 A tree of the file structure of the disk is given. Capital letters denote directory names, lowercase letters denote file names.
List the names of directories of the 1st, 2nd, 3rd levels. Specify the path to letter. txt from the root directory. Specify the path to the letter1.doc file from the root directory, and to the letter2.doc file - from the WORK directory. Specify full file names
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letter. txt and letters. doc if the file structure is stored on drive C.
Solution. 1st level catalogs COMPUTER, WORK, UROK. 2nd level directories - IBM, APPLE, DOCUMENT, PRINT. 3rd level directories - D0C1, D0C2.
The path to letter. txt from the root directory: \WORK\PRINT. Path to letterl file. doc from the root directory: \W0RK\D0CUMENT\D0C2. Path to letter2.doc file from W0RK:\D0CUMENT\D0C2 directory.
Full filenames are letter. txt and letters. doc:
C:\WORK\PRINT\letter. txt and
C:\W0RK\D0CUMENT\D0C2\letterl. doc.
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A tree of a hierarchical file structure on a magnetic disk is given. Capital letters denote directory names, lowercase letters denote file names:
Find errors in the file structure.
A tree of a hierarchical file structure on a magnetic disk is given. Capital letters denote directory names, lowercase letters denote file names:
List directories of the 1st, 2nd, 3rd levels, if any. Specify the paths from the root directory to each of the files.
\COUNTRY\USA\INFO\culture. txt; \COUNTRY\USA\washington. txt; \COUNTRY\RUSSIA\moscow. txt; \COUNTRY\RUSSIA\INFO\industry. txt; \COUNTRY\RUSSIA\INFO\culture. txt
The paths from the root directory to some files stored on the magnetic disk are indicated. Capital letters denote directory names, lowercase letters denote file names: \BOX\LETTER\peter. txt; \BOX\LETTER\kate. txt; \LETTER\WORK\april. txt; \LETTER\WORK\may. txt; \LETTER\FREND\SCHOOL\mary. txt; \LETTER\FREND\sport. txt. Display the file structure as a tree.
Decide tasks: ■ № 1
A double-sided floppy disk has a capacity of 800 KB. How many tracks are on one side of a floppy if each track contains 20 sectors of 0.5 KB each. Solution".
1) 800:2=400 Kbytes - diskette size;
2) 20 * 0.5 = 10 Kb - the volume of all sectors;
3) 400:10=40 - tracks. Answer: 40 tracks.
What is the capacity of each sector of a 360 KB double-sided floppy if each side of the floppy is divided into 40 tracks with 18 sectors per track?
Solution:
1) 40*18=720 sectors on the disk;
2) 360:720=0.5 KB - sector size. Answer: 0.5 KB.
The paths from the root directory to some files stored on the magnetic disk are indicated. Capital letters denote directory names, lowercase letters denote file names: \SPORT\SKI\russia. txt; \SPORT\SKI\germany. txt; \SPORT\SKATE\finland. txt; \COMPUTER\IBM\INFO\pentium. txt; \COMPUTER\INFO\ibm. txt. Display the file structure as a tree.
The speed and reliability of modern recorders will be the envy of any Formula 1 car. ComputerBild explains how data ends up on CDs, DVDs, and Blu-ray discs.
Recording music and movies on optical media is a familiar process, like using magnetic cassettes twenty years ago, only much cheaper. What is the difference between the types of media and how information is recorded on them?
Stamping and burning
In the industrial production of discs with music, films or games, data is written to the media by stamping - this process is similar to the manufacture of gramophone records. Information on disks is stored in the form of tiny depressions. Computer and consumer DVD recorders perform this task differently - they use a laser beam.
The first recordable optical media were CD-Rs with write-once capability. When data is stored on such discs, the laser beam heats the working layer of the disc, which consists of a dye, to about 250 ° C, which causes a chemical reaction. Dark opaque spots are formed at the place of laser heating. This is where the word "burn" comes from.
Similarly, the transfer of data to a DVD with the possibility of a single write. But on the surface of rewritable CDs, DVDs and Blu-ray discs, dark dots do not form. The working layer of these drives is not a dye, but a special alloy. When heated by a laser to about 600 °C, it passes from the crystalline state to the amorphous state. The areas exposed to the laser have a darker color, and hence other reflective properties.
Information carriers
Home recording discs are the same thickness (1.2 mm) and the same diameter (12 or 8 cm) as commercially recorded discs. Optical media have a multilayer structure.
Substrate. The basis for discs, which is made of polycarbonate, is a transparent, colorless and fairly resistant to external influences polymer material.
working layer. For recordable CDs and DVDs, it consists of an organic dye, and for rewritable CDs, DVDs (RW, RAM) and Blu-ray discs, it is formed by a special alloy that can change the phase state. The working layer is surrounded on both sides by an insulating substance.
reflective layer. To create a layer from which the laser beam is reflected, aluminum, silver or gold are used.
protective layer. They are only available on CDs and Blu-ray discs. It is a hard lacquer.
Label. A layer of varnish is applied on top of the disc - the so-called label. This layer is able to absorb moisture, so that the ink that is on the surface of the media during printing dries quickly.
Differences between CDs, DVDs and Blu-ray discs
These media have different characteristics. First of all - different capacity. A Blu-ray disc can store up to 25 GB of data, a DVD can store 5 times less information, and a CD can store 35 times less information. Blu-ray drives use a blue laser to read and write data. Its wavelength is about 1.5 times shorter than in red laser DVD and CD drives. This allows you to record a much larger amount of information on an equal disk surface.
Media formats
The following types of optical media are currently on the market.
CD-R. Recordable CDs can hold up to 700 MB of information. There are also discs with a capacity of 800 MB, but they are not supported by all recorders and consumer players. 8 cm miniCDs can store 210 MB of data.
CD-RW. Rewritable media has the same storage capacity as CD-R.
DVD-R/DVD+R. Recordable DVDs hold 4.7 GB of information. miniDVD with a diameter of 8 cm - 1.4 GB.
DVD-R DL/DVD+R DL. The prefix DL means Dual Layer (DVD-R) or Double Layer (DVD+R), which corresponds to a two-layer media. Capacity - 8.5 GB. Up to 2.6 GB is placed on an eight-centimeter disk.
DVD-RW/DVD+RW. Single-layer media of this type are capable of withstanding several hundred write cycles. Like DVD record-once, rewritable discs have a capacity of 4.7 GB, while 8 cm discs have a capacity of about 1.4 GB.
DVD-RAM. These media have the same storage capacity as single layer DVDs. There are also dual-layer discs that hold twice as much information. DVD-RAM can withstand up to 100,000 write cycles, but only a few DVD players work with these discs. Data is written not on a spiral track, but in sectors on ring tracks, as on hard disk platters. The marks that define the boundaries of the sectors are clearly visible on the surface of DVD-RAM - by their presence it is easy to distinguish this type of media from others.
BD-R/BD-R DL. An abbreviation used to refer to recordable Blu-ray discs. BD-R media has one working layer that holds 25 GB of data. BD-R DL are equipped with two working layers, so their capacity is 2 times higher.
BD-RE/BD-RE DL. Rewritable Blu-ray discs are rated for 1000 write cycles. They can store as much data as non-rewritable media.
"Plus and minus"
The presence of "plus" and "minus" media is a consequence of the long-standing war of formats. In the beginning, the computer industry relied on the "plus" format, while consumer electronics manufacturers promoted the "minus" format as the standard for recordable DVDs. Modern recorders and players support both formats.
None of them has clear advantages over the other. Both media types use the same materials. Therefore, there are no significant differences between "plus" and "minus" disks of the same manufacturer.
Recording quality
The recording quality of media of the same format can vary significantly. Much depends on the recorder model used. The recording speed also plays an important role: the lower it is, the fewer errors and the higher the quality.
Recorder and media compatibility
Not every recorder is able to record on discs of all formats without exception. There are certain restrictions.
CD recorders. Cannot work with DVD and Blu-ray discs.
DVD recorders. They burn CDs and DVDs, but do not support Blu-ray format.
Blu-ray recorders. They record both on Blu-ray and on any CD and DVD.
Disc signatures
The media on which the information is posted should be signed immediately so as not to be confused later. This can be done in different ways.
Blanks with the possibility of printing. The top side of these discs is varnished. On such a surface, you can print text and images using inkjet printers and MFPs equipped with a special tray. Discs don't differ in price from ordinary ones.
Signature with a recorder. The recorder's support for LightScribe or Labelflash technology allows one-color images and text to be applied to the surface of specially designed media. True, the process can take up to 30 minutes, and the cost of LightScribe discs is about twice the cost of conventional discs. Labelflash-enabled media will cost even more.
New LabelTag technology. Developed by the manufacturer of recorders Lite-On and involves the application of text on the working surface of the disc. This eliminates the need for special media. However, disk space is wasted because the text is applied directly to the track. Yes, and the inscription is well read only if the areas with text contrast brightly with empty fragments.
Signature made by hand. To do this, you need to purchase special markers with a soft, rounded at the end of the rod and solvent-free ink. Other markers may corrode the disc surface and cause scratches.
Use of stickers. You can print stickers on any printer. However, sticking them is not recommended, as this often leads to damage to the surface of the disk, and hence to data loss. It may happen that the label comes off while playing the disc. In this case, the optical drive is likely to be damaged.
Data retention period
Disk manufacturers often state that data on the media will be stored for 30 years or more. However, this duration is only possible under ideal storage conditions - in a dry, cool and dark place. The recording quality must be high.
With frequent use, the life of self-recorded discs will be greatly reduced. During playback, media is exposed to high temperatures and mechanical stress. Data loss can also be caused by scratches or dirt.
Transferring information to disk
All optical media, with the exception of DVD-RAM, has a spiral track that runs from the center of the disc to the outer edge. Information is recorded on this track by a laser beam. When burned, the laser beam forms tiny spots on the reflective layer - pits (from the English pit - pit). Areas that were not exposed to the laser are called lands (from the English land - surface). When translated into binary storage language, pit is 0 and land is 1.
When playing a disc, information is read using a laser. Due to the different reflectivity of pits and lands, the drive recognizes dark and light areas of the disc. Thus, a sequence of zeros and ones is read from the media, which make up all physical files without exception.
With the development of technology, there was a gradual decrease in the wavelength of the laser beam used in the recorders, which made it possible to significantly improve the accuracy of focusing. The track has become narrower, the pits are smaller, and a larger amount of data is placed on an equal area of \u200b\u200bthe disk. The shorter the wavelength, the smaller the distance between the working layer and the laser.
Media production
Using DVD as an example, ComputerBild explains how optical media is produced and how the production of other types of discs differs.
1. To mold a plastic substrate, polycarbonate, heated to 350 ° C, is fed into a mold by injection molding. A microscopic spiral track in the form of a groove (Pre-Groove) is created on the surface of the base using a matrix. Not only is data written to this track, it also contains a signal to synchronize the recorder's spindle drive. After cooling the substrate to 60 °C, a central hole is made, then the temperature is reduced to 25 °C and further processing begins. DVDs usually consist of two polycarbonate layers, each 0.6 mm thick. For single-layer recordable DVDs, only one of the layers is further processed as described in steps 2-3, while for dual-layer DVDs, both. CDs and Blu-ray discs have only one layer 1.2 mm thick.
2. The working layer of recordable CDs and DVDs is created by centrifugation. With the help of a dispenser, the dye is injected onto the surface of a disk rotating at a constant speed in the region of the central hole and is evenly distributed over the surface of the carrier.
3. The reflective layer is deposited on the disc by ion-plasma sputtering. In a vacuum chamber, an aluminum, silver or gold plate is bombarded with charged ions, which knock out metal atoms from it - it remains on the surface of the working layer of the blank. For rewritable CDs, DVDs and Blu-ray discs, all working and reflective layers are created using ion-plasma sputtering. In four chambers, the first insulator layer, the working layer, the second insulator layer and the reflective layer are successively applied to the disc. When producing Blu-ray discs, these operations are performed in reverse order.
4. Two polycarbonate bases are glued together. For CDs and Blu-ray discs, instead of the second base, a lacquer coating is applied, which is dried under an ultraviolet lamp. The varnish coating of Bly-ray discs is particularly durable, while DVDs do not need a protective layer of varnish.
5. At the last stage, the blanks receive a label, and an absorbent layer of varnish is applied to the discs that can be printed on a printer.
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COURSE WORK
MAGNETIC AND OPTICAL STORAGE CARRIERS AND THE POSSIBILITY OF THEIR USE IN THE PRACTICE OF ORGANIZATIONS
Introduction
Conclusion
List of used sources and literature
Introduction
Relevance
The information society is characterized by many features, one of which is that information becomes the most important factor in the development of society.
Preservation, development and rational use of the documentary resource are of great importance for any society and state.
A distinctive feature of the current stage of human development is the presentation of information not only in printed and other analog forms, but also in electronic, digital form, which makes it possible to create, store, organize access and use electronic documents in a fundamentally different way.
In nature, the natural carrier of information is human memory. And yet, since ancient times, a person has been using extraneous auxiliary means for storing information, which at the beginning were the most primitive (stones, branches, feathers, beads). Historical milestones in the development of information storage media were the creation of writing, the invention of papyrus first, then parchment and paper, and then printing.
In our time, the number of material carriers has increased significantly. One thing remains unchanged requirements for storage, as well as the volume of stored information with the development of mankind only increases, and the exact time when the information will depreciate is usually not known.
As a result, society strives to always choose the best media in order to preserve important information. But is it so easy to choose a material carrier?
The purpose of the work is to characterize magnetic and optical documents, as well as to substantiate their use in the work of organizations.
Object of study: magnetic and optical documents.
Subject of study: the use of magnetic and optical documents in the work of organizations.
1. Ways of storing information
1.1 The oldest ways of storing information
The first carriers of information were the walls of caves in the Paleolithic era. At first, people painted on the walls of caves, stones and rocks, such drawings and inscriptions are called petroglyphs. The most ancient rock carvings and petroglyphs (from the Greek. petros - stone and glyphe - carving) depicted animals, hunting and domestic scenes. Among the most ancient images on the walls of the caves of the Paleolithic era are the impressions of human hands, and the random interweaving of wavy lines, pressed into the wet clay with the fingers of the same hand. It is noteworthy how vivid, vivid were the images of animals in the caves of the late period of the ancient Stone Age. Their creators were well aware of the behavior of animals, their habits. They noticed in their movements such lines that elude the modern observer. It is noteworthy that, while depicting animals, the ancient masters used rock irregularities, depressions, and protrusions to model their bodies, resembling the outlines of the figures. The image, as it were, has not yet separated from the space surrounding it, has not become independent.
The people of the ancient Stone Age did not know the ornament. On the images of animals and people made of bone, rhythmically repeating strokes or zigzags, similar to an ornament, are sometimes visible. But, looking closely, you see that this is a symbol for wool, bird feathers or hair. Just as the image of an animal “continues” the rocky background, so these ornament-like motifs have not yet become independent, conditional figures separated from the thing, which can be applied to any surface. It should be assumed that the oldest information carriers served not only as a simple decoration, but rock paintings were intended to convey information or combined these functions.
One of the first materials available was clay. Clay is a material carrier of writing signs, which had sufficient strength (safety of information), besides, it was inexpensive and easily accessible, and plasticity, ease of recording made it possible to increase the efficiency of recording, it was possible to easily, clearly and distinctly depict writing signs. Natural writing material was found by the ancient inhabitants of Mesopotamia, who lived in the very south of this country - the Sumerians. The main natural wealth of this region was clay: local residents built their dwellings, temples of the gods from it, made dishes, lamps, and coffins from it. According to the ancient Sumerian myth, even man was created from clay. The reserves of this material were practically inexhaustible. Therefore, in the region of the Southern Mesopotamia, clay tablets became the material carrier of signs of writing, which were widely used here already at the beginning of the 3rd millennium BC. e.
The ability to write effectively contributes to the emergence of writing. More than five thousand years ago (the achievement of the Sumerian civilization, the territory of modern Iraq) writing on clay appeared (no longer drawings, but icons and pictograms similar to letters).
Clay tablets became the material basis for highly developed writing. In the second half of the III millennium BC. e. in Sumerian literature, a wide variety of genres were represented: myths and epic tales in verse, hymns to the gods, teachings, fables about animals, proverbs and sayings. American Sumerologist Samuel Cramer was lucky enough to open the world's oldest "library catalog", placed on a tablet 6.5 cm long and about 3.5 cm wide. The scribe managed to write the names of 62 literary works on this tiny tablet. “At least 24 titles from this catalog refer to works that have partially or completely come down to us,” writes S.Ya. Kramer.
More accessible writing material was invented in ancient Rome. These were special wax tablets that mankind has been using for over 1500 years. These tablets were prepared from wood or ivory. From the edges of the board, at a distance of 1-2 cm, a recess was made by 0.5--1 cm, and then it was filled with wax around the entire perimeter. They wrote on the tablet, applying signs to the wax with a sharp metal stick - a stylus, which was pointed on one side, and its other end had the shape of a spatula and could erase the inscription. Such wax plates were folded with wax inside and connected in two (diptych) or three (triptych) pieces or several pieces with a leather strap (polyptych) and a book was obtained, a prototype of medieval codes and a distant ancestor of modern books. In the ancient world and the Middle Ages, wax tablets were used as notebooks, for household notes and for teaching children to write. There were similar waxed tablets in Russia and they were called tsers.
In a hot climate, the records on wax tablets were short-lived, but some of the original wax tablets have survived to this day (for example, with the records of the French kings). Of the Russian tsers, the so-called Novgorod Code, dating from the 11th century, has been preserved. - This is a polyptych consisting of four wax pages.
A huge step forward was the use of papyrus, introduced by the ancient Egyptians. The oldest papyrus scroll dates back to the 25th century BC. e. Later, the Greeks and Romans adopted the papyrus script from the Egyptians. They wrote on it with a special pen.
Papyrus is a writing material spread in Egypt and throughout the Mediterranean, for the manufacture of which a plant of the sedge family was used.
The raw material for the manufacture of papyrus was the reed growing in the Nile River valley. The papyrus stalks were peeled, the core was cut lengthwise into thin strips. The resulting strips were laid out overlapping on a flat surface. Another layer of strips was laid out on them at a right angle and placed under a large smooth stone, and then left under the scorching sun. After drying, the papyrus sheet was polished and smoothed with a shell or a piece of ivory. The sheets in their final form looked like long ribbons and therefore were preserved in scrolls, and at a later time they were combined into books.
In ancient times, papyrus was the main writing material throughout the Greco-Roman world. The production of papyrus in Egypt was very large. And for all its good qualities, papyrus was still a fragile material. Papyrus scrolls could not have been kept for more than 200 years. Papyri have survived to this day only in Egypt, solely due to the unique climate of this area.
As a material carrier of information, papyrus was used not only in Ancient Egypt, but also in other countries of the Mediterranean, and in Western Europe - up to the 11th century. And the last historical document written on papyrus was the message of the Pope at the beginning of the 20th century.
The disadvantage of this carrier was that over time it darkened and broke. An additional disadvantage was that the Egyptians imposed a ban on the export of papyrus abroad.
The shortcomings of information carriers (clay, papyrus, wax) stimulated the search for new carriers. This time the principle "everything new - well forgotten old" worked. People began the production of writing material from animal skin - parchment. Parchment gradually replaced papyrus. The advantages of the new medium are high reliability of information storage (strength, durability, did not darken, did not dry out, did not crack, did not break), reusability (for example, in a surviving prayer book of the 10th century, scientists found several layers of records made up and down, erased and cleaned , and with the help of X-rays, the oldest treatise of Archimedes was discovered there). Books on parchment - palimpsests (from the Greek language rblYamshzufpn - a manuscript written on parchment according to a washed out or scraped off text).
The name of the material comes from the city of Pergamon, where this material was first made. From antiquity to the present day, parchment is known among Jews under the name "gwil", as a canonical material for recording the Sinai Revelation in handwritten Torah scrolls. On the more common type of parchment “klaf”, passages from the Torah for tefil and mezuzah were also written. For the manufacture of these varieties of parchment, only the skins of kosher animal species are used.
Parchment is untanned dressed animal skin - sheep, calf or goat.
According to the Greek historian Ctesias in the 5th c. BC e. leather has long been used as a material for writing by the Persians. From where, under the name "diftera", she passed to Greece, where, along with papyrus, processed sheep and goat skins were used for writing.
Another material of plant origin, used mainly in the equatorial zone (in Central America since the 8th century, on the Hawaiian Islands) was tapa. It was made of paper mulberry wood, in particular, from bast, bast. The bast was washed, cleaned of irregularities, then beaten with a hammer, smoothed and dried.
The ancient Germans wrote their runic texts on beech tablets (Buchenholz), hence the word "Buch", a book. The signs were applied by scratching (Writan), from where the English verb write comes from, to write (of the same root as the German ritzen, to scratch).
The Romans, in the earliest period of their history, when writing was only coming into use, wrote on a wooden bast (liber): the same word they began to call a book. The information carriers of the Roman script have not been preserved on this material, but birch-bark letters can, apparently, serve as the closest analogue.
Birch bark - widespread since the 12th century
In search of more practical media, people tried to write on wood, its bark, leaves, leather, metals, bones. In countries with a hot climate, dried and varnished palm leaves were often used. In Russia, the most common material for writing was birch bark - certain layers of birch bark.
The so-called birch bark letter, a piece of birch bark with scratched signs, was found by archaeologists on July 26, 1951 during excavations in Novgorod. There was also written evidence that birch bark was used in ancient Russia for writing - Joseph Volotsky mentions this in a story about the monastery of Sergius of Radonezh.
Archaeologists have even found a miniature birch bark book of 12 pages, 5 x 5 cm in size, in which double sheets are sewn along the fold. Preparing the birch bark for the recording process was not difficult. Previously, it was boiled, then the inner layer of the bark was scraped off and cut off at the edges. The result was the base material of the document in the form of a ribbon or rectangle. The inner side of the birch bark, which is smoother, was usually used for writing. The letters were rolled up into a scroll. In this case, the text was on the outside. The texts of birch bark letters were squeezed out using a special tool - a stylus made of iron, bronze or bone.
Due to the shortcomings of the previous carriers, the Chinese emperor Liu Zhao ordered that a worthy replacement be found for them. While in the Western world there was competition between wax tablets, papyrus and parchment in China in the 2nd century BC. paper was invented.
At first, paper in China was made from defective silkworm cocoons, then they began to make paper from hemp. Then in 105 AD. Cai Lun began making paper from crushed mulberry fibers, wood ash, rags, and hemp. He mixed all this with water and laid out the resulting mass on a mold (wooden frame and bamboo sieve). After drying in the sun, he smoothed this mass with the help of stones. The result is strong sheets of paper. Even then, paper was widely used in China. After Cai Lun's invention, the papermaking process improved rapidly. They began to add starch, glue, natural dyes, etc. to increase strength.
At the beginning of the 7th century, the method of making paper becomes known in Korea and Japan. And after another 150 years, through prisoners of war, he gets to the Arabs. Papermaking, born in China, is slowly moving to the West, gradually infiltrating the material culture of other peoples.
1.2 Invention of modern storage media
Since the 19th century, in connection with the invention of new ways and means of documenting (photo, film, audio documentation, etc.), many fundamentally new carriers of documented information have become widespread. Depending on their qualitative characteristics, as well as on the method of documentation, they can be classified as follows:
paper;
photographic media;
mechanical sound recording media;
magnetic media;
optical (laser) discs and other promising information carriers.
The most important material carrier of information is still paper. There are currently hundreds of different types of paper and paper products on the domestic market. When choosing paper for documentation, it is necessary to take into account the properties of the paper, due to the technological process of its production, compositional composition, degree of surface finish, etc.
Any paper made in the traditional way is characterized by certain properties that must be taken into account in the documentation process. These key features and indicators include:
compositional composition, i.e. composition and type of fibers (cellulose, wood pulp, flax, cotton and other fibers), their percentage, degree of grinding;
weight of paper (weight of 1 sq. m of paper of any grade). The mass of paper produced for printing is from 40 to 250 g/sq. m;
paper thickness (can be from 4 to 400 microns);
density, degree of porosity of paper (amount of paper pulp in g / cm Ё);
structural and mechanical properties of the paper (in particular, the direction of orientation of the fibers in the paper, light transmission, transparency of the paper, deformation under the influence of moisture, etc.);
paper surface smoothness;
light fastness;
weediness of paper (the result of using polluted water in its production) and some other properties of paper.
Depending on the properties, paper is divided into classes (for printing, for writing, for typing, decorative, packaging, etc.), as well as types (typographic, offset, newspaper, coated, writing, cartographic, Whatman paper, document, etc.) .). So, paper with a surface density of 30 to 52 g/m¦ and with a predominance of wood pulp in its compositional composition is called newsprint. Printing paper has a surface density of 60 to 80 g/m¦ and is made on the basis of wood pulp. Cartographic paper has even greater density (from 85 to 160 g/m¦). For technical documentation, high-grade white drawing paper is used, which is produced on the basis of mechanically processed rags. For printing banknotes, bonds, bank checks and other important financial documents, paper is used that is resistant to mechanical stress. It is made on the basis of linen and cotton fibers, often with watermarks94.
Perforated tapes were used for mechanical recording of encoded information and its further use in information retrieval systems, in punching computers. They were made of thick paper with a thickness of about 0.1 mm and a width of 17.5; 20.5; 22.5; 25.5 mm.
Paper formats are of great importance in document management and documentation management. Back in 1833, a single sheet of paper was established in Russia, and in 1903 the union of paper manufacturers adopted 19 of its formats. But at the same time, there were numerous formats that arose spontaneously at the initiative of paper mills and based on the wishes of consumers95. In the 1920s, after the decision of the Bolshevik leadership to switch to the metric system, paper formats were also streamlined, and subsequently GOST 9327-60 "Paper and paper products. Consumer formats" was adopted. The new formats were based on the paper size system first proposed by the German standardization organization DIN around 1920. In 1975, this system became an international standard (ISO 216) by being adopted by the International Organization for Standardization. It also operates in Russia.
The ISO 216 standard consists of three series: A, B and C. Series (row) A is set as the main one. Here, each sheet of paper has a width equal to the result of dividing its length by the square root of two (1: 1.4142). The area of the main format (A0) is 1 m¦, and its sides are 841x1189 mm. The remaining formats are obtained by successively dividing the previous format in half, parallel to its smaller side. As a result, all the resulting formats are geometrically similar. Each format is indicated by two characters: the letter A, indicating that it belongs to the A series, and a number indicating the number of divisions of the original A0 format.
ISO 216 A-series formats:
4A0 1682x2378; 2A0 1189x1682; A0 841x1189; A1 594x841; A2 420x594; A3 297x420;
A4 210x297; A5 148x210; A6 105x148; A7 74x105; A8 52x74; A9 37x52; A10 26x37.
B-series formats are used when the A-series does not have a suitable format. The B-series format is the geometric mean between the An and A(n+1) formats.
The C-series formats standardize envelopes. The C-series format is the geometric mean between the A and B series formats of the same number. For example, a document on an A4 sheet fits well into a C4 envelope.
Taking into account paper sizes according to the ISO system, copiers were created, i.e. tied to a 1:v2 ratio. This principle is also used in film and photo labs. The copiers are equipped with the appropriate scaling tools most commonly used, for example:
71% v0.5 А3>А4
141% v2 A4>A3 (also A5> A4)
ISO paper sizes are now widely used in all industrialized countries, with the exception of the United States of America and Canada, where other, albeit very similar, formats are common in office work: "Letter" (216x279 mm), "Legal" (216x356 mm) , "Executive" (190x254 mm) and "Ledger/Tabloid" (279x432 mm)97.
Certain types of paper are designed specifically for reprographic processes. These are mainly light-sensitive paper carriers. Among them are thermal paper (thermoset and thermocopy paper); diazo paper (diazo type or blueprint paper) sensitive to ultraviolet rays; tracing paper - transparent, durable, pure cellulose paper intended for copying drawings; multilayer paper for electrospark copying, etc.
Paper with a thickness of over 0.5 mm and a mass of 1 sq. m more than 250 g is called cardboard. Cardboard can be single-layer and multi-layer. In office work, it is used, in particular, for the manufacture of covers for primary sets of documents (cases), registration cards, etc.
Until recently, cardboard perforated media of digital coded information - punched cards - were widely used. They were rectangles measuring 187.4x82.5 mm and were made of thin, mechanically strong cardboard.
On the basis of machine punched cards, aperture cards were made - cards with a built-in frame of microfilm or a piece of non-perforated film. They were usually used to store and search for figurative and graphic technical documentation and patent information.
Photographic materials are flexible films, plates, papers, fabrics. They are essentially multilayer polymer systems consisting, as a rule, of: a substrate (base), on which an underlayer is applied, as well as a light-sensitive emulsion layer (silver halide) and an antihalation layer.
Color photographic materials have a more complex structure. They also contain blue-, yellow-, green-, red-sensitive layers. The development of multi-layered colored materials in the 1950s was one of the qualitative leaps in the history of photography, predetermining the rapid development and widespread use of color photography.
Among the most important characteristics of photographic materials, in particular, photographic films, are: light sensitivity, graininess, contrast, color sensitivity.
Film is a photographic material on a flexible transparent substrate with holes on one or both edges - perforations. Historically, the first photosensitive tape media were paper-based. The cellulose nitrate tape used at first was a very combustible material. However, already in 1897, the German scientist Weber made a film with a non-combustible base from cellulose triacetate, which was widely used, including in the domestic film industry. Subsequently, the substrate began to be made of polyethylene terephthalate and other elastic polymeric materials.
Compared to photographic film, film is usually made up of more layers. A sublayer is applied to the substrate, which serves to fix the photosensitive layer (or several layers) on the base. In addition, motion picture film usually has an anti-halation, anti-curl, and protective layer.
Films are available in black and white and color. They are also divided into:
negative;
positive (for contact and projection printing);
negotiable (can be used to obtain negatives and positives);
countertype (for copying, for example, for mass production of film copies);
hydrotype;
phonogram (for photographic recording of sound).
Black and white photographic film, 16 and 35 mm wide, is the most common medium for microfilm making. The main types of microfilm are roll and cut microfilm. Cut microfilm is a part of a roll film with a length of at least 230 mm, on which up to several dozen frames are placed. Microcards, microfiches and ultramicrofiches are actually flat format microfilm. In particular, a microfiche is a sheet of photographic film in the format of 105x148 mm.
For more than a century of history of mechanical sound recording, both the materials and the form of sound information carriers have repeatedly changed. Initially, these were phonographic rollers, which were hollow cylinders with a diameter of about 5 cm and a length of about 12 cm. They were covered with the so-called "hardened wax" on which the sound track was applied. The phono rolls wore out quickly, it was almost impossible to replicate them. Therefore, quite naturally, they soon turned out to be supplanted by gramophone records.
The gramophone records had to meet very stringent requirements, since in the process of playing a sound recording, the tip of the needle presses on the bottom of the groove with a force of about 1 t / cm¦. The first gramophone record, recorded in 1888, was a zinc disc with an engraved phonogram. Then gramophone records began to be cast from celluloid, rubber, ebonite. However, plastic discs based on polyvinyl chloride and vinylite turned out to be much cheaper, more elastic and durable. They also had the best sound quality.
Gramophone records were made by pressing, stamping or casting. The original record was a wax disc, and later a metal (nickel) disc coated with a special lacquer (lacquer disc)99.
According to the type of recording, gramophone records produced in our country were divided into ordinary, long-playing and stereophonic. Abroad, in addition, quadraphonic records and video records were developed. In addition, gramophone records are classified by size, rotational speed, subject of recording. In particular, stereophonic records, the production of which in the USSR began in 1958, as well as long-playing ones, were produced in the format (diameter) 174, 250 and 300 mm. The frequency of their rotation was usually 33 rpm.
Since the early 1990s the production of gramophone records in Russia has actually ceased, giving way to other, better and more efficient methods of sound recording (electromagnetic, digital)
1.3 Effect of media type on document durability and value
The transfer of documented information in time and space is directly related to the physical characteristics of its material carrier. Documents, being a mass social product, have a relatively low durability. During their operation in the operating environment, and especially during storage, they are exposed to numerous negative influences due to temperature changes, humidity, light, biological processes, etc. For example, currently there are about 400 species of fungi and insects found on documents and books that can infect paper, tracing paper, fabrics, wood, leather, metal, film and other materials. Therefore, it is no coincidence that the problem of the durability of material information carriers has attracted the attention of participants in the documentation process at all times. Already in antiquity, there was a desire to record the most important information on such relatively durable materials as stone and metal. For example, the laws of the Babylonian king Hammurabi were carved on a stone pillar. And today these materials are used for long-term preservation of information, in particular, in memorial complexes, at burial sites, etc. In the process of documentation, there was a desire to use high-quality, durable paints and inks. To a large extent, thanks to this, many important textual historical monuments, documents of the past have come down to us. And, on the contrary, the use of short-lived material media (palm leaves, wooden planks, birch bark, etc.) led to the irretrievable loss of most text documents of the distant past.
However, solving the problem of durability, a person immediately had to deal with another problem, which was that durable storage media were, as a rule, more expensive. So, books on parchment were often equated in price to a stone house or even to a whole estate, were made into a will, along with other property, and in libraries they were chained to the wall. Therefore, we constantly had to look for the optimal ratio between the durability of the material information carrier and its cost. This problem is still very important and relevant.
The currently most common material carrier of documented information - paper - is relatively cheap, accessible, meets the necessary requirements for its quality, etc. However, at the same time, paper is a combustible material, it is afraid of excessive moisture, mold, sunlight, and needs certain sanitary and biological conditions. The use of insufficient quality ink, paints lead to the gradual fading of the text on paper. According to experts, the first crisis period in the history of a paper document began in the middle of the 19th century. It was associated with the transition to the manufacture of paper from wood, with the use of synthetic dyes, with the widespread use of typewriting and copying tools. As a result, the durability of a paper document has been reduced from thousands to two hundred - three hundred years, i.e. in order. Particularly short-lived are documents made on paper of low quality types and grades (newsprint, etc.).
At the end of the 20th century, with the development of computer technology and the use of printers to display information on paper, the problem of the durability of paper documents arose again. The fact is that many modern printouts of texts on printers are water-soluble and fade. More durable inks, in particular, for inkjet printers, of course, are also more expensive, and therefore less accessible to the mass consumer. The use of "pirated" reloaded cartridges and toners in Russia only exacerbates the situation.
Material carriers of documented information thus require appropriate conditions for their storage. However, this has not always been observed and observed. As a result, documents from departmental archives for state storage in our country come with defects. In the 1920s, the number of defects reached 10-20%, since the 1950s it began to decrease from 5 to 1%, in the 1960s-1980s it was at the level of 0.3-0.5% (although in absolute terms this amounted to 1-2.5 million documents). In the 1990s, the storage of documents in departmental archives deteriorated again, as in the first decades of the existence of Soviet power. All this results in significant material losses, since in archives and libraries it is necessary to create and maintain expensive laboratories that are engaged in the restoration of paper media. We also have to make archival copies of documents with fading text, etc.
In the Soviet Union, at one time, a government program was even created that provided for the development and production of domestic durable paper for documents, special stable writing and copying tools, as well as limiting the use of short-lived materials for creating documents with the help of standards. In accordance with this program, by the 1990s, special durable papers for office work were developed and began to be produced, designed for 850 and 1000 years. The composition of domestic writing media was also adjusted. However, further implementation of the program in modern Russian conditions turned out to be impossible due to radical socio-political and economic changes, as well as as a result of a very rapid change in the methods and means of documentation.
The problem of durability and economic efficiency of material information carriers has become especially acute with the advent of audiovisual and machine-readable documents, which are also subject to aging and require special storage conditions. Moreover, the process of aging of such documents is multilateral and differs significantly from the aging of traditional information carriers.
First, audiovisual and computer-readable documents, as well as documents on traditional media, are subject to physical aging associated with the aging of the material medium. Thus, the aging of photographic materials manifests itself in a change in the properties of their photosensitivity and contrast during storage, in an increase in the so-called photographic veil, and in an increase in the fragility of films. In color photographic materials, there is a violation of the color balance, i.e. fading, which manifests itself as a distortion of colors and a decrease in their saturation. Particularly unstable were film and photo documents on nitrofilm, which, in addition, was also an extremely combustible material. The first color film and photo documents faded very quickly. It should be noted that, in general, the shelf life of color film documents is several times shorter than that of black-and-white ones, due to the instability of color image dyes. At the same time, the film carrier is a relatively durable material. It is no coincidence that in archival practice, microfilms still remain an important way to store backup copies of the most valuable documents, since, according to experts, they can be stored for at least 500 years.
The service life of gramophone records is determined by their mechanical wear, depends on the intensity of use, storage conditions. In particular, plastic discs (phonograph records) can deform when heated.
Unlike traditional text and graphic documents, audiovisual and machine-readable documents are subject to technical aging associated with the level of development of equipment for reading information. The rapid development of technology leads to the fact that problems and sometimes insurmountable obstacles arise for the reproduction of previously recorded information, in particular, from phono rollers, records, films, since the production of equipment for their reproduction has either ceased long ago, or the existing equipment is designed to work with material media, with other technical characteristics. For example, it is now difficult to find a computer to read information from 5.25" floppy disks, although it has only been five years since they were supplanted by 3.5" floppies.
Finally, there is logical aging, which is related to the content of information, software and standards of information preservation. Modern digital coding technologies allow, according to scientists, to store information "almost forever." However, this requires periodic rewriting, for example, CDs - in 20-25 years. First, it's expensive. And, secondly, computer technology is developing so rapidly that there is a discrepancy between the equipment of old and new generations. For example, when American archivists one day decided to get acquainted with the 1960 census data stored on magnetic media, it turned out that this information could be reproduced using only two computers in the whole world. One of them was in the US and the other in Japan.
Technical and logical aging leads to the fact that a significant amount of information on electronic media is irretrievably lost. In order to prevent this, the US Library of Congress, in particular, has set up a special division where all devices for reading information from obsolete electronic media are kept in working order.
Currently, an intensive search for information-capacious and at the same time sufficiently stable and economical media continues. It is known, for example, about the experimental technology of the Los Alamos Laboratory (USA), which makes it possible to record encoded information of 2 GB (1 million typewritten pages) with an ion beam on a piece of wire only 2.5 cm long. At the same time, the predicted durability of the carrier is estimated in 5 thousand years with very high wear resistance. For comparison: in order to record information from all paper media of the Archival Fund of the Russian Federation, only 50 thousand such pins would be required, i.e. 1 box115. At one of the scientific conferences, also held in the USA, the "eternal disk" Rosetta made of nickel was demonstrated. It allows you to save in analog form up to 350,000 pages of text and drawings for several thousand years.
Thus .... After comparing material media, we can say that with the development of science and technology, new, more advanced, information-capacious, reliable and affordable media of documented information will appear, which will replace outdated media that we use now.
2. Characteristics of magnetic and optical storage media
2.1 Material media
The very first magnetic recording medium used in Poulsen devices at the turn of the 19th and 20th centuries was steel wire up to 1 mm in diameter. At the beginning of the 20th century, rolled steel tape was also used for this purpose. At the same time (in 1906) the first patent for a magnetic disk was issued. However, the quality characteristics of all these carriers were very low. Suffice it to say that the production of a 14-hour magnetic recording of reports at the International Congress in Copenhagen in 1908 required 2500 km or about 100 kg of wire.
It was not until the second half of the 1920s, when powder magnetic tape was invented, that magnetic recording began to be widely used. Initially, magnetic powder was deposited on a paper substrate, then on cellulose acetate, until the use of high-strength polyethylene terephthalate (lavsan) material as a substrate began. The quality of the magnetic powder has also been improved. In particular, iron oxide powders with the addition of cobalt, metal magnetic powders of iron and its alloys began to be used, which made it possible to increase the recording density by several times.
In 1963, the so-called cassette recording was developed by Philips, which made it possible to use very thin magnetic tapes. In compact cassettes, the maximum tape thickness is only 20 µm with a width of 3.81 mm. In the late 1970s microcassettes appeared with a size of 50 x 33 x 8 mm, and in the mid-1980s. - picocassettes - three times less than microcassettes.
Since the early 1960s magnetic disks have been widely used - primarily in computer storage devices. A magnetic disk is an aluminum or plastic disk with a diameter of 30 to 350 mm, coated with a magnetic powder working layer several microns thick. In a disk drive, as in a tape recorder, information is recorded using a magnetic head, only not along the tape, but on concentric magnetic tracks located on the surface of a rotating disk, usually on both sides. Magnetic disks are hard and flexible, removable and built into a personal computer. Their main characteristics are: information capacity, access time to information and reading speed in a row.
Aluminum magnetic disks - hard (hard drive) non-removable disks - are structurally combined in a computer in a single unit with a disk drive. They are arranged in packages (stacks) from 4 to 16 pieces. Writing data to a hard magnetic disk, as well as reading, is carried out at speeds up to 7200 rpm. The disk capacity reaches over 9 GB. These media are designed for permanent storage of information that is used when working with a computer (system software, application software packages, etc.).
Flexible plastic magnetic disks (floppy disks, from the English floppy - freely hanging) are made of flexible plastic (dacron) and are placed one by one in special plastic cassettes. A floppy disk cassette is called a floppy disk. The most common floppy disks are 3.5" and 5.25" in diameter. The capacity of one floppy disk is usually from 1.0 to 2.0 MB. However, a 3.5-inch floppy disk with a capacity of 120 MB has already been developed. In addition, floppy disks are produced that are designed to work in conditions of increased dust and humidity.
The so-called plastic cards, which are devices for the magnetic method of storing information and managing data, have found wide application, primarily in banking systems. They are of two types: simple and intelligent. In simple cards there is only a magnetic memory that allows you to enter data and change them. In smart cards, which are sometimes called smart cards (from the English smart - smart), in addition to memory, a microprocessor is also built in. It makes it possible to make the necessary calculations and makes plastic cards multifunctional.
It should be noted that, in addition to magnetic, there are other ways to record information on a card: graphic recording, embossing (mechanical extrusion), bar coding, and since 1981, also laser recording (on a special laser card that allows you to store a large volume information, but still very expensive).
To record sound in digital voice recorders, in particular, minicards are used, which have a similarity to floppy disks with a memory capacity of 2 or 4 MB and provide recording for 1 hour.
Currently, material magnetic recording media are classified:
by geometric shape and size (the shape of a tape, disk, card, etc.);
by the internal structure of the media (two or more layers of different materials);
according to the method of magnetic recording (carriers for longitudinal and perpendicular recording);
by type of recorded signal (for direct recording of analog signals, for modulation recording, for digital recording).
Technologies and material carriers of magnetic recording are constantly being improved. In particular, there is a tendency to increase the density of information recording on magnetic disks with a decrease in its size and a decrease in the average access time to information.
2.2 Optical storage media
The development of material carriers of documented information as a whole follows the path of a continuous search for objects with high durability, large information capacity with minimal physical dimensions of the carrier. Since the 1980s, optical (laser) discs have become more and more widespread. These are plastic or aluminum discs designed to record and reproduce information using a laser beam.
For the first time, optical recording of sound programs for domestic purposes was carried out in 1982 by Sony and Philips in laser CD players, which began to be designated by the abbreviation CD (Compact Disc). In the mid-1980s, CD-ROMs (Compact Disc - Read Only Memory) were created. Since 1995, rewritable optical CDs have been used: CD-R (CD Recordable) and CD-E (CD Erasable).
Optical discs usually have a polycarbonate or glass heat-treated base. The working layer of optical disks is made in the form of the thinnest films of fusible metals (tellurium) or alloys (tellurium-selenium, tellurium-carbon, tellurium-selenium-lead, etc.), organic dyes. The information surface of optical discs is covered with a millimeter layer of durable transparent plastic (polycarbonate). In the process of recording and playback on optical discs, the role of the signal converter is performed by a laser beam focused on the working layer of the disc into a spot with a diameter of about 1 μm. As the disk rotates, the laser beam follows along the disk track, the width of which is also close to 1 μm. The possibility of focusing the beam into a small spot makes it possible to form marks on the disk with an area of 1–3 μm¦. Lasers (argon, helium-cadmium, etc.) are used as a light source. As a result, the recording density is several orders of magnitude higher than the limit provided by the magnetic recording method. The information capacity of an optical disk reaches 1 GB (with a disk diameter of 130 mm) and 2-4 GB (with a diameter of 300 mm).
Unlike magnetic methods of recording and playback, optical methods are non-contact. The laser beam is focused on the disc by an objective that is up to 1 mm away from the carrier. This virtually eliminates the possibility of mechanical damage to the optical disc106. For a good reflection of the laser beam, the so-called "mirror" coating of the discs with aluminum or silver is used.
Magneto-optical compact discs of the RW (Re Writeble) type have also been widely used as an information carrier. Information is recorded on them by a magnetic head with the simultaneous use of a laser beam. The laser beam heats up a point on the disk, and the electromagnet changes the magnetic orientation of that point. Reading is performed by a laser beam of lower power.
In the second half of the 1990s, new, very promising carriers of documented information appeared - digital universal video discs DVD (Digital Versatile Disk) of the DVD-ROM, DVD-RAM, DVD-R type with a large capacity (up to 17 GB). The increase in their capacity is associated with the use of a laser beam of a smaller diameter, as well as two-layer and two-sided recording.
According to the technology of application, optical, magneto-optical and digital CDs are divided into 3 main classes:
discs with permanent (non-erasable) information (CD-ROM). These are plastic CDs with a diameter of 4.72 inches and a thickness of 0.05 inches. They are made using an original glass disc, on which a photo-recording layer is applied. In this layer, the laser recording system forms a system of pits (marks in the form of microscopic depressions), which is then transferred to replicated copy discs. Reading information is also carried out by a laser beam in the optical drive of a personal computer. CD-ROMs usually have a capacity of 650 MB and are used for recording digital audio programs, computer software, etc.;
discs that allow one-time recording and multiple playback of signals without the possibility of erasing them (CD-R; CD-WORM - Write-Once, Read-Many - recorded once, counted many times). They are used in electronic archives and data banks, in external computer drives. They are a base made of a transparent material on which a working layer is applied;
reversible optical discs that allow multiple recording, playback and erasing of signals (CD-RW; CD-E). These are the most versatile discs that can replace magnetic media in almost all areas of application. They are similar to write-once discs, but contain an operating layer in which the physical write processes are reversible. The manufacturing technology of such discs is more complicated, so they are more expensive than record-once discs.
Magnetic media (tapes, disks, cards, etc.) are characterized by high sensitivity to external electromagnetic influences. They are also subject to physical aging, wear of the surface with the applied magnetic working layer (the so-called "shedding"). Magnetic tape stretches over time, resulting in distortion of the information recorded on it. information carrier document
Compared to magnetic media, optical discs are more durable, since their service life is determined not by mechanical wear, but by the chemical and physical stability of the environment in which they are located. Optical discs also need to be stored at stable room temperatures and with relative humidity within the limits specified for magnetic tapes. Excessive humidity, high temperature and its sharp fluctuations, polluted air are contraindicated for them. Of course, optical discs should also be protected from mechanical damage. It should be borne in mind that the most vulnerable is the "non-working" painted side of the disk.
3. Use of magnetic and optical storage media
3.1 Use of media in the practice of organizations
The carrier in the practice of the organization is important. The type of carrier is important, its durability. This choice depends on the type of electronic document and its storage period. The most common way of storing information resources in organizations is by storing files on hard drives of computers or servers. Sometimes it becomes necessary to transfer electronic documents to external media. To store large and complex databases and other information resources (for example, scientific, technical or publishing), in order not to violate the integrity of data, it is better to use capacious electronic media: optical disks, removable hard drives, RAID arrays, etc.
For archival storage of electronic documents within 5 years, any modern electronic information carriers (magnetic diskettes, magnetic tapes, magnetic, magneto-optical and optical disks) are quite reliable.
For long-term storage of electronic documents on external media, the best solution would be to use optical CDs. They are unpretentious in storage and quite reliable for 15-20 years. After this period, you will inevitably have to either rewrite files to another type of media (because it will be impossible to read information from a CD), or convert electronic documents to other formats and also rewrite them to more modern and capacious media.
The second and third aspects of preservation are much more difficult. They are associated with rapid change and obsolescence of computer hardware and software. Over time, devices that read information from external media wear out and become obsolete. So, for example, 5-inch magnetic diskettes disappeared, and after them, computers were no longer equipped with disk drives for reading them. In the near future, a similar fate awaits 3-inch floppy disks, and many modern PC models are already being released without disk drives for them. Devices for reading information from optical discs are also likely to change over time. The approximate life cycle of such technologies is 10-15 years. These technological changes must be taken into account when organizing the long-term storage of electronic documents.
3.2 The use of magnetic and optical media in the practice of organizations
Reproduction of electronic documents depends primarily on the software used: OS, DBMS, browsers, and other applications. Changing the software platform can lead to the complete loss of the document due to the inability to view it. However, for the bulk of office and financial electronic documents with a shelf life of up to 5 years, this factor is not so significant: the software life cycle is estimated at 5-7 years. In the short term, to access and reproduce most text, graphics and video documents (but not databases or complex design systems and multimedia), the use of such converters is sufficient.
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