home / Installation and configuration/ Characteristics of magnetic and optical media. Types of storage media, their classification and characteristics Magnetic storage media "

Characteristics of magnetic and optical information carriers. Types of storage media, their classification and characteristics Magnetic storage media "

The very first magnetic recording medium on which information was recorded in Poulsen's devices at the turn of the 19th-20th centuries was steel wire up to 1 mm in diameter. At the beginning of the XX century, for these purposes was also used rolled steel strip. However, the quality characteristics of these carriers were very low. Suffice it to say that 2500 km of wire weighing about 100 kg was required to produce a 14-hour magnetic recording of the lectures at the International Congress in Copenhagen in 1908. In addition, in the process of using wire and steel tape, the intractable problem of joining their separate pieces arose. For example, the knotted wire did not pass through the magnetic head. In addition, she was easily confused, and the thin steel band cut her hands. Steel magnetic disk, the first patent for which was issued back in 1906 was not applied at that time 1.

Only from the second half of the 1920s, when it was invented powder magnetic tape, the large-scale use of magnetic recording began. A patent for the technology of applying a ferromagnetic powder to a film was obtained in 1928 by Fritz Pfeimer in Germany. Initially, the magnetic powder was applied to a paper substrate, then to cellulose acetate, until the use of high-strength

1 Vasilevskii Yu. A. Magnetic recording media. M., 1989.S. 5-6.

material - polyethylene terephthalate (lavsan). The quality of the magnetic powder was also improved. In particular, iron oxide powders with the addition of cobalt, chromium oxide, metal magnetic powders of iron and its alloys began to be used, which made it possible to increase the recording density several times. The working layer is applied to the substrate by vacuum deposition or electrolytic deposition in the form of a magnetic varnish, which consists of magnetic powder, binder, solvent, plasticizer and various additives.

In addition to the flexible base and the working magnetic layer, the tape can have additional layers: protective - on the surface of the working layer and antifriction - on the back of the tape, in order to protect the working layer from mechanical wear, increase the mechanical strength of the tape and to improve its sliding on the magnetic surface. heads. The anti-friction layer also removes electrical charges that accumulate on the magnetic tape. The intermediate (sublayer) between the base and the working layer serves to improve the adhesion of the working and antifriction layers to the base.

Unlike mechanical sound recording media, magnetic tape is suitable for multiple recordings of information. The number of such records is very large and is limited only by the mechanical strength of the magnetic tape itself.

The first tape recorders, which appeared in the 1930s, were reel-to-reel. In them, the magnetic tape was wound on spools. And in the beginning, these were huge bobbins 1 inch (25.4 mm) wide. During recording and playback, the tape was rewound from a full reel to an empty one.

In 1963, Philips developed the so-called cassette recording, which made it possible to use very thin magnetic tapes. Their maximum thickness is only 20 microns with a width of 3.81 mm. In cassette recorders, both reels are in a special compact cassette and the end of the film is pre-secured to the empty spool. In other words, here the magnetic tape and the cassette are a single functional mechanism. Recording on compact cassettes - two-way. The total recording time is usually 60, 90 and 120 minutes.

In the late 1970s. appeared microcassettes size 50x33x8 mm, that is, the size of a matchbox, for portable voice recorders and telephones with an answering machine, and in the mid-1980s. - picocassettes- three times less microcassettes.

Since 1952, magnetic tape has been used for recording and storing information in electronic computers. The advantage of magnetic tape is the ability to record with increased density due to the fact that the total surface area of the magnetic layer of the tape is much higher than that of other types of media, and is limited only by the length of the tape. Cassette Tape Drives - cartridges reach a capacity of several TB, and in the near future their capacity will be tens of TB. The tape drive mechanisms for cartridges are called streamers(from English, stream - stream). In principle, they are similar to a tape recorder.

However, magnetic tape also has a serious drawback. It does not allow direct access to the recorded information. To do this, the tape must first be rewound to the desired location, which significantly increases the time for reading information from it. Magnetic tape cassettes (cartridges) are also characterized by their large dimensions. Therefore, at present they are mainly used in backup systems in data centers, in enterprises, in large data centers, as well as for storing information in servers and desktop workstations, where reliability, stability of operation, large capacity, relatively low cost. Backup systems allow you to ensure the safety of information in the event of errors, malfunctions or natural disasters.

On a magnetic tape, you can record not only audio, but also video information. Video tape its structure is similar to tape for audio recording. However, its working layer usually has a more complex structure. The fact is that high-frequency video signals are recorded at the very surface of the working layer. Small metal particles can be used for them. Low frequencies, on the other hand, are better transmitted by large particles, which are advisable to be placed in depth. Therefore, the working layer of a magnetic tape for video filming can consist of two layers. The magnetic tape for video documentation is also loaded into special cassettes, which provide it with protection from mechanical stress, pollution and fast loading into video equipment. Widespread in the 1980s - 1990s. videotapes have now given way to more promising video media.

At first, electronic computers also used magnetic drums. In particular, in the domestic large electronic calculating machine (BESM-6) magnetic drums weighing about 8 kg were used, but with a memory capacity of only 1 MB.

Since the early 1960s. widespread use, primarily in computer storage devices, received magnetic disks. These are aluminum or plastic discs with a diameter of 30 to 350 mm, covered with a magnetic powder working layer several microns thick. At first, the magnetic coating consisted of iron oxide, later - of chromium dioxide.

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, time of access to information and speed of reading in a row.

Non-removable hard drives in a computer are structurally combined in a single unit with a disk drive. They are assembled into packages on one axis. The pack of discs is placed in a sealed case, which provides the necessary cleanliness and constant pressure of dust-free air. At present, instead of air, the use of helium inert gas as a filler has begun, which allows, due to its lower density, to significantly increase energy efficiency.

Each disc contains the same number of consecutive tracks (tracks). The width of the magnetic track is approximately 1 µm. The first model of the hard disk, created in 1973, had 30 tracks of 30 sectors, which coincidentally coincided with the caliber "30/30" of the famous Winchester hunting rifle and gave rise to the slang name of hard magnetic disks - "Winchester", "Winchesters". The tracks are concentric circles corresponding to the areas of remanent magnetization created by the magnetic heads. In turn, each of the tracks is divided into sequentially located sectors.

The main trend in the development of hard drives is a gradual increase in the recording density, accompanied by an increase in the rotation speed of the spindle head and a decrease in the access time to information, and ultimately - an increase in productivity. Disk capacity, which originally reached several GB, reached 10 TB by the middle of the second decade of the 21st century (annual growth of computer hard disk capacity is 35-40 percent). Placing such a volume of information became possible on disks with a perpendicular recording method, which appeared in 2007. In the near future, this method will increase the capacity to 85 TB (you can record 86 million color photographs or 21.5 thousand films).

Hard drives are designed for permanent storage of information, incl. necessary when working with a computer (system software, application packages, etc.). On the basis of hard disks, external storage devices with a capacity of up to several TB are also produced.

Flexible plastic magnetic disks (floppy disks, from English, floppy - free hanging) were made of artificial film - mylar, covered with wear-resistant ferrolacquer, and were placed one by one in special hard plastic cases - cassettes, which provide mechanical protection for the media. The floppy disk cassette is called diskette.

The first floppy disk appeared in 1967. It had a diameter of 8 inches and a storage capacity of 100 KB. In 1976, the size of the floppy disk was reduced to 5.25 inches, and in 1980, Soni developed the 3.5-inch floppy disk and floppy drive, which were mainly produced in the following decades.

To read and write information, a special electronic-mechanical device is used - a disk drive, where a floppy disk is placed. The floppy disk has a central hole for the spindle of the disk drive, and in the case there is a hole that can be closed with a metal shutter for access to the magnetic heads, through which information is read and written. Recording on a floppy disk is carried out according to the same principle as in a tape recorder. There is also a direct mechanical contact of the head with the magnetic working layer, which leads to a relatively rapid wear of the material carrier.

The capacity of one 3.5-inch floppy disk was typically 1.0 to 2.0 MB. Standard floppy disks had a capacity of 1.44 MB. However, 3.5-inch floppy disks have been developed with capacities up to 250 MB.

Floppy disks turned out to be quite finicky media. They are less wear-resistant than hard drives and are susceptible to magnetic fields and elevated temperatures. All this often led to the loss of recorded data. Therefore, floppy disks were used primarily for operational storage of documented information. They are now being superseded by more reliable and efficient flash storage media.

In the last quarter of the XX century in many countries of the world, and since the 1990s. - and in Russia, the so-called plastic cards, representing a device for a magnetic method of storing information and data management.

The predecessors of plastic cards were cards made of cardboard in order to confirm the creditworthiness of the holder outside the bank. In 1928, one of the American companies began to produce metal cards measuring 63 by 35 mm. They were embossed with the owner's name, city, state, and other information. Such cards were issued to regular customers in large stores. When paying for goods, the seller rolled the card through a special machine, as a result of which the letters and numbers squeezed out on it were imprinted on the sales receipt. This check with the handwritten purchase amount was then sent to the bank for redemption. The very first modern credit card, on the basis of which the VISA payment system arose, was issued in 1958 by Bank of America.

Plastic cards consist of three layers: a polyester base, on which a thin working layer is applied, and a protective layer. Polyvinyl chloride is usually used as a base, which is easy to process, resistant to temperature, chemical and mechanical stress. However, in some cases, the basis for magnetic cards is the so-called pseudo-plastic - thick paper or cardboard with double-sided lamination.

The working layer (ferromagnetic powder) is applied to the plastic by hot stamping in the form of separate narrow strips. According to their physical properties and scope of application, magnetic strips are divided into two types: high-ercetive and low-erythritic. Highly ercetic stripes are black. They are resistant to magnetic fields. Higher energy is needed to record them. They are used as credit cards, driving licenses, etc., that is, in cases where increased durability and security are required. Low-EMC magnetic stripes are brown. They are less secure, but easier and faster to write. Used on cards with limited expiration dates.

The protective layer of magnetic plastic cards consists of a transparent polyester film. It is designed to protect the working layer from wear. Occasionally, anti-counterfeiting and anti-copying coatings are used. The protective layer provides up to two tens of thousands of write and read cycles.

It should be noted that, in addition to magnetic, there are other ways of recording information on a plastic card: graphic recording, embossing (mechanical extrusion), bar-coding, laser recording.

Nowadays, electronic chips are increasingly used in plastic cards instead of magnetic stripes. Such cards, in contrast to simple magnetic ones, began to be called intelligent or smart cards(from English, smart -smart). The microprocessor built into them allows you to store a significant amount of information, makes it possible to make the necessary calculations in the system of bank and trade payments, thus turning plastic cards into multifunctional information carriers.

By the way of access to the microprocessor (interface), smart cards can be:

- with a contact interface (i.e., when performing an operation, the card is inserted into the electronic terminal);
- with a dual interface (they can act both contact and non-contact, that is, data exchange between the card and external devices can be carried out via a radio channel).

The sizes of plastic cards are standardized. In accordance with the international standard ISO-7810, their length is 85.595 mm, width - 53.975 mm, thickness - 3.18 mm.

The scope of application of magnetic plastic and pseudo-plastic cards, as well as smart cards, is quite extensive. In addition to banking systems, they are used as a compact information carrier, an identifier for automated accounting and control systems, certificates, passes, Internet cards, mobile SIM cards, transport tickets, electronic (biometric) passports, etc.

Tangible magnetic recording media are constantly being improved along with electromagnetic documentation technologies. There is a tendency to an increase in the density of information recording on magnetic media with a decrease in their size and a reduction in the time of access to information. Technologies are being developed which, in the not too distant future, will make it possible to increase the memory capacity of a standard medium by several thousand times in comparison with currently operating devices. And in the longer term, a carrier is expected to appear, where individual atoms will play the role of magnetic particles. As a result, its capacity, according to the developers, will exceed the existing standards by billions of times.

Vasilevsky Yu. A. Decree. op. S. 11, 225, 227-228; Levin V.I. op. by S. 23-24.
Manukov S. How not to become a card idiot // Company. 2009. No. 27-28. P. 52.
Fradkin V. Past, present and future of information carriers // Computer Price. 2003. No. 46.

The very first magnetic recording medium, which was used in Poulsen's apparatus at the turn of the 19th and 20th centuries, was steel wire with a diameter of up to 1 mm. At the beginning of the 20th century, rolled steel strips were also used for these purposes. 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 2500 km, or about 100 kg of wire, were required to produce the 14-hour magnetic recording of the lectures at the International Congress in Copenhagen in 1908.

It was only in the second half of the 1920s, when magnetic flux-cored tape was invented, that magnetic recording began to be widely used. Initially, the magnetic powder was applied to a paper substrate, then to cellulose acetate, until the use of high-strength polyethylene terephthalate (lavsan) material as a substrate began. The quality of the magnetic powder was also 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 several times.

In 1963, Philips developed the so-called cassette recording, which made it possible to use very thin magnetic tapes. Compact cassettes have a maximum tape thickness of only 20 µm and a width of 3.81 mm. In the late 1970s. micro-cassettes appeared, measuring 50 x 33 x 8 mm, and in the mid-1980s. - pico-cassettes - three times less than micro-cassettes.

Since the early 1960s. Magnetic disks are widely used, primarily in computer storage devices. A magnetic disk is an aluminum or plastic disk with a diameter of 30 to 350 mm, covered 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, time of access to information and speed of reading in a row.

Aluminum magnetic disks - hard (Winchester) non-removable disks - are structurally combined in a computer in a single block with a disk drive. They are arranged in packages (stacks) from 4 to 16 pieces. Data writing 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 intended for permanent storage of information that is used when working with a computer (system software, application packages, etc.).

Flexible plastic magnetic disks (floppy disks, from the English floppy - free hanging) are made of flexible plastic (lavsan) and are placed one by one in special plastic cassettes. A floppy disk cartridge is called a floppy disk. The most common floppy disks are 3.5 and 5.25 inches. The capacity of one floppy disk is usually 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, there are floppy disks designed for work in conditions of increased dustiness and humidity.

The so-called plastic cards, which are devices for a 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 it. In smart cards, which are sometimes called smart cards (from the English smart - smart), in addition to memory, there is also a built-in microprocessor. It makes it possible to carry out the necessary calculations and makes plastic cards multifunctional.

It should be noted that, in addition to magnetic, there are other methods of recording information on the 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 amount information, but still very expensive).

To record sound in digital dictaphones, in particular, mini-cards are used, which resemble floppy disks with a memory volume of 2 or 4 MB and provide recording for 1 hour.

Currently, tangible magnetic recording media are classified:

by geometric shape and size (shape of a tape, disk, card, etc.);

by the internal structure of the carriers (two or more layers of different materials);

by the method of magnetic recording (media for longitudinal and perpendicular recording);

by the type of the recorded signal (for direct recording of analog signals, for modulation recording, for digital recording).

The technologies and material carriers of magnetic recording are constantly being improved. In particular, there is a tendency towards an increase in the density of information recording on magnetic disks with a decrease in its size and a decrease in the average time of access to information.

Information carrier (information carrier) - any material object used by a person to store information. This can be, for example, stone, wood, paper, metal, plastics, silicon (and other types of semiconductors), tape with a magnetized layer (in reels and cassettes), photographic material, plastic with special properties (for example, in optical discs) and etc., etc.

The information carrier can be any object from which it is possible to read (read) the information available on it.

Information carriers are used for:

records;
storage;
reading;
transmission (distribution) of information.

Often, the information carrier itself is placed in a protective shell, which increases its safety and, accordingly, the reliability of storing information (for example, paper sheets are placed in a cover, a memory chip is placed in plastic (smart card), a magnetic tape is placed in a case, etc.) ...

Electronic media include media for one-time or re-recording (usually digital) in an electrical way:

optical discs (CD-ROM, DVD-ROM, Blu-ray Disc);
semiconductor (flash memory, floppy disks, etc.);
CD-disks (CD - Compact Disk, compact disk), which can store up to 700 MB of information;
DVD-disks (DVD - Digital Versatile Disk, digital versatile disk), which have a significantly larger information capacity (4.7 GB), since the optical tracks on them are thinner and more densely packed;
HR DVD and Blu-ray discs, the information capacity of which is 3-5 times higher than that of DVD discs, due to the use of a blue laser with a wavelength of 405 nanometers.

Electronic media have significant advantages over paper ones (paper sheets, newspapers, magazines):

by the volume (size) of stored information;
by the unit cost of storage;
on the efficiency and efficiency of providing relevant (intended for short-term storage) information;
if possible, providing information in a form convenient for the consumer (formatting, sorting).

There are also disadvantages:

fragility of readers;
weight (mass) (in some cases);
dependence on power supplies;
the need for a reader / writer for each type and format of media.

A hard (magnetic) disk drive, HDD, HMDD), a hard disk is a storage device (information storage device) based on the principle of magnetic recording. It is the main data storage device in most computers.

Unlike a "floppy" disk (floppy disk), information in a hard disk drive is recorded on hard plates covered with a layer of ferromagnetic material - magnetic disks. The HDD uses one or more plates on one axis. The readheads in the operating mode do not touch the surface of the plates due to the interlayer of the incoming air flow formed at the surface during rapid rotation. The distance between the head and the disc is several nanometers (in modern discs about 10 nm), and the absence of mechanical contact ensures a long service life of the device. In the absence of rotation of the disks, the heads are located at the spindle or outside the disk in a safe ("parking") zone, where their abnormal contact with the surface of the disks is excluded.

Also, unlike a floppy disk, a storage medium is usually combined with a drive, a drive and an electronics unit. Such hard drives are often used as non-removable storage media.

Optical (laser) discs are currently the most popular storage media. They use the optical principle of recording and reading information using a laser beam.

DVDs can be dual-layer (8.5 GB capacity), with both layers having a reflective surface that carries information. In addition, the information capacity of DVDs can be doubled further (up to 17 GB), since information can be recorded on both sides.

There are three types of optical disc drives:

without the ability to write - CD-ROM and DVD-ROM (ROM - Read Only Memory, read-only memory). CD-ROMs and DVD-ROMs contain information that was recorded on them during the manufacturing process. Writing new information to them is impossible;
write-once and multiple-read - CD-R and DVD ± R (R - recordable). Information can be recorded on CD-R and DVD ± R discs, but only once;
rewritable - CD-RW and DVD ± RW (RW - Rewritable). On CD-RW and DVD ± RW discs, information can be recorded and erased many times.

Key Features of Optical Drives:

disk capacity (CD - up to 700 MB, DVD - up to 17 GB)
the speed of data transfer from the carrier to the RAM - measured in fractions that are multiples of the speed of 150 Kbytes / sec for CD drives;
access time - the time required to search for information on the disc, measured in milliseconds (for CD 80–400 ms).

Currently, 52x-speed CD-drives are widely used - up to 7.8 MB / sec. CD-RW discs are burned at a lower speed (for example, 32x). Therefore, CD-drives are marked with three numbers "read speed x write speed CD-R x write speed CD-RW" (for example, "52x52x32").
DVD drives are also labeled with three numbers (for example, "16x8x6").

Subject to the rules of storage (storage in cases in an upright position) and operation (without causing scratches and dirt), optical media can store information for tens of years.

Flash memory - refers to semiconductors of electrically programmable memory (EEPROM). Due to technical solutions, low cost, large volume, low power consumption, high speed of operation, compactness and mechanical strength, flash memory is embedded in digital portable devices and storage media. The main advantage of this device is that it is non-volatile and does not need electricity to store data. All information stored in flash memory can be read an infinite number of times, but the number of complete write cycles, unfortunately, is limited.

Flash memory has its advantages in front of other drives (hard drives and optical drives), and its own shortcomings, which you can get acquainted with from the table below.

Drive type	Advantages	disadvantages
HDD	Large amount of stored information. High speed of work. Cheap storage of data (per 1 MB)	Large dimensions. Vibration sensitivity. Noise. Heat dissipation
Optical disc	Convenience of transportation. The cheapness of information storage. Replication possibility	Small volume. You need a reader. Restrictions on operations (reading, writing). Low speed of work. Vibration sensitivity. Noise
Flash memory	High speed of data access. Economical energy consumption. Vibration resistance. Convenience of connecting to a computer. Compact dimensions	Limited number of write cycles

The need to store any information in humans appeared in prehistoric times, for which a vivid example is the rock art, which has survived to this day. Rock carvings can rightfully be called the most durable storage medium at the moment, although there are some difficulties with portability and ease of use. With the advent of computers (and PCs in particular), the development of capacious and easy-to-use storage media has become especially relevant.

Paper carriers

The first computers used punched cards and perforated paper tape wound on spools, called punched tape. Its progenitors were automated looms, in particular the Jacquard machine, the final version of which was created by the inventor (after whom it was named) in 1808. Perforated plates were used to automate the filament feeding process:

Punched cards are cardboard cards that used a similar method. There were many varieties of them, both with holes, which were responsible for the "1" in the binary code, and textual. The most common was the IBM format: the size of the map was 187x83 mm, the information on it was located in 12 lines and 80 columns. In modern terms, one punch card held 120 bytes of information. To enter information, punched cards had to be submitted in a specific sequence.

Punched tape uses the same principle. Information is stored on it in the form of holes. The first computers, created in the 40s of the last century, worked both with data entered using punched tape in real time, and used some kind of random access memory, mainly using cathode ray tubes. Paper media were actively used in the 20-50s, after which they gradually began to be replaced by magnetic media.

Magnetic media

In the 50s, active development of magnetic carriers began. The phenomenon of electromagnetism (the formation of a magnetic field in a conductor when a current is passed through it) was taken as a basis. The magnetic carrier consists of a ferromagnetic coated surface and a read / write head (wound core). A current flows through the winding, a magnetic field of a certain polarity appears (depending on the direction of the current). The magnetic field acts on the ferromagnet and the magnetic particles in it are polarized in the direction of the field and create remanent magnetization. To write data to different areas, a magnetic field of different polarity is applied, and when reading the data, zones are recorded in which the direction of the remanent magnetization of the ferromagnet changes. The first such media were magnetic drums: large metal cylinders coated with a ferromagnet. Reading heads were installed around them.

After them, a hard drive appeared in 1956, it was the 305 RAMAC of IBM, which consisted of 50 disks with a diameter of 60 cm, was comparable in size to a large refrigerator of the modern Side-by-Side format and weighed a little less than a ton. Its volume was incredible for those times 5 MB. The head moved freely over the surface of the disk and the operating speed was higher than that of magnetic drums. Loading the 305 RAMAC on the plane:

Volume began to expand rapidly, and in the late 1960s, IBM released a high-speed, dual-drive, 30MB drive. Manufacturers worked hard to reduce the size and by 1980 the hard drive was the size of a 5.25-inch drive. Since that time, the design, technology, volume, density and dimensions have undergone colossal changes and the most popular form factors have become 3.5, 2.5 inches, at least 1.8 inches, and volumes already reach ten terabytes on a single carrier.

For some time, the IBM Microdrive format was also used, which was a miniature hard drive in the form factor of a CompactFlash memory card. type II. Released in 2003, later sold to Hitachi.

In parallel, magnetic tape developed. It appeared along with the release of the first American commercial computer UNIVAC I in 1951. Again, IBM tried its best. The magnetic tape was a thin plastic strip with a magnetically sensitive coating. It has been used in a wide variety of form factors since then.

From reels, tape cartridges to compact cassettes and VHS tapes. They were used in computers from the 70s to the 90s (already in much smaller quantities). Often a plug-in tape recorder was used as an external medium to a PC.

Tape drives called Streamers are still used today, mainly in industry and big business. At the moment, bobbins of the standard are used. Linear Tape-Open (LTO), and the record was set this yearIBM and FujiFilm, having managed to write 154 terabytes of information onto a standard reel. The previous record was 2.5 terabytes, LTO 2012.

Another type of magnetic media is floppy disks or floppy disks. Here a layer of ferromagnet is applied to a flexible, lightweight base and placed in a plastic case. Such media were simple to manufacture and were inexpensive. The first floppy disk had a form factor of 8 inches and appeared in the late 60s. The creator is again IBM. By 1975, the capacity had reached 1 MB. Although the popularity of the floppy was earned thanks to immigrants from IBM, who founded their own company Shugart Associates also released a 5.25-inch floppy disk in 1976 with a capacity of 110 KB. By 1984, the capacity was already 1.2 MB, and Sony pushed in advance with a more compact 3.5-inch form factor. Such floppy disks can still be found in many homes.

Iomega released the Bernoulli Box magnetic disc cartridges in the 1980s, with a capacity of 10 and 20 MB, and in 1994 - the so-calledZip size 3.5 inches with a volume of 100 MB, until the end of the 90s they were quite actively used, but they were too tough to compete with CDs.

Optical media

Optical media are disc-shaped and read using optical radiation, usually a laser. The laser beam is directed to a special layer and reflected from it. When reflected, the beam is modulated by the smallest notches on a special layer; during registration and decoding of these changes, the information recorded on the disk is restored. The first optical recording technology using light-transmitting media was developed by David Paul Gregg in 1958 and patented in 1961 and 1990, and in 1969 Philips created the so-called LaserDisc, in which light was reflected. The LaserDisc was first shown to the public in 1972 and went on sale in 1978. It was similar in size to vinyl records and was intended for films.

In the seventies, the development of new optical media began, as a result of which Philips and Sony introduced the CD (Compact Disk) format in 1980, which was first demonstrated in 1980. CDs and equipment went on sale in 1982. Originally used for audio, took up to 74 minutes. In 1984, Philips and Sony created the CD-ROM (Compact Disc Read Only Memory) standard for all types of data. The volume of the disk was 650 MB, later - 700 MB. The first discs that could be recorded at home, and not at the factory were released in 1988 and were called CD-R (Compact Disc Recordable) and CD-RWs, which allow multiple rewriting of data on a disc, appeared already in 1997.

The form factor did not change, the recording density increased. In 1996, the DVD (Digital Versatile Disc) format appeared, which had the same shape and diameter of 12 cm, and a volume of 4.7 GB or 8.5 GB for a dual layer. To work with DVDs, the corresponding drives were released, backward compatible with CDs. Several more DVD standards were released in the following years.

In 2002, two different and incompatible next generation optical disc formats were introduced to the world: HD DVD and Blu-ray Disc (BD). In both cases, a blue laser with a wavelength of 405 nm is used to write and read data, which made it possible to further increase the density. HD DVD can store 15GB, 30GB or 45GB (one, two or three layers), Blu-ray 25, 50, 100 and 128GB. The latter became more popular and in 2008 Toshiba (one of the creators) abandoned HD DVD.

Semiconductor media

In 1984, Toshiba introduced semiconductor media called NAND flash memory, which became popular a decade after its invention. The second variant of NOR was proposed by Intel in 1988 and is used to store program codes such as BIOS. NAND is now used in memory cards, flash drives, SSDs, and hybrid hard drives.

NAND technology allows you to create chips with a high recording density, it is compact, less power-consuming to use and has a higher operating speed (compared to hard drives). The main disadvantage at the moment is the rather high cost.

Cloud storage

With the development of the worldwide network, the increase in speeds and mobile Internet, numerous cloud storages have appeared, in which data is stored on multiple servers distributed over the network. The data is stored and processed in a so-called virtual cloud and the user has access to them if there is Internet access. Physically, servers can be located remotely from each other. There are both specialized services like Dropbox and options from software or device companies. Microsoft has OneDrive (formerly SkyDrive), Apple's iCloud, Google Drive, and so on.

Floppy disk drives: principle of operation, specifications, main components. Hard disk drives: form factors, principle of operation, types, main characteristics, modes of operation. Configuring and formatting magnetic disks. Utilities for maintenance of hard magnetic disks. Logical structure and format of magneto-optical and compact discs. CD-R (RW), DVD-R (RW), ZIP drives: principle of operation, main components, technical characteristics. Magneto-optical drives, streamers, flash drives. Review of the main modern models.

The student should know:

The principle of operation and the main components of the FDD drive;

Characteristics and modes of operation of the hard disk drive;

The principle of operation of drives of magneto-optical and compact disks;

Optical and magneto-optical disc formats;

The student should be able to:

Record information on various media;

Use hard disk maintenance software;

Determine the main characteristics of drives;

Lesson objectives:

To acquaint students with the main components of information storage devices.

Examine the types of storage media and their characteristics.

Education of information culture of students, attentiveness, accuracy, discipline, perseverance.

The development of cognitive interests, self-control skills, the ability to take notes.

Course of the lesson:

Theoretical part.

Data storage on magnetic media

Almost all personal computers store information on media that use magnetic or optical principles. Magnetic storage drives the binary data into small, magnetized metal particles that are “patterned” on a flat disk or tape. This magnetic "pattern" can subsequently be decoded into a binary data stream.

Magnetic media — hard drives and floppy drives — are based on electromagnetism. Its essence lies in the fact that when an electric current is passed through a conductor, a magnetic field is formed around it (Fig. 1). This field acts on the ferromagnetic substance trapped in it. When the direction of the current changes, the polarity of the magnetic field also changes. The phenomenon of electromagnetism is used in electric motors to generate forces acting on magnets that are mounted on a rotating shaft.

However, there is also the opposite effect: an electric current arises in a conductor that is exposed to an alternating magnetic field. When the polarity of the magnetic field changes, the direction of the electric current also changes (Fig. 2).

The read / write head in any disk drive consists of a U-shaped ferromagnetic core and a coil (winding) wound around it, through which an electric current can flow. When current is passed through the winding, a magnetic field is created in the core (magnetic circuit) of the head (Fig. 3). When the direction of the flowing current is switched, the polarity of the magnetic field also changes. In essence, the heads are electromagnets, the polarity of which can be changed very quickly by switching the direction of the passed electric current.

Rice. 1. When a current is passed through a conductor, a magnetic field is formed around it

Rice. 2. When a conductor is moved in a magnetic field, an electric current is generated in it

Rice. 3. Read / write head

The magnetic field in the core partially spreads into the surrounding space due to the presence of a gap “sawn through” at the base of the letter U. If another ferromagnet is located near the gap (the working layer of the carrier), then the magnetic field is localized in it, since such substances have a lower magnetic resistance than air ... The magnetic flux crossing the gap is closed through the carrier, which leads to the polarization of its magnetic particles (domains) in the direction of the field action. The direction of the field and, therefore, the remanent magnetization of the carrier depends on the polarity of the electric field in the head winding.

Flexible magnetic disks are usually made on lavsan, and hard disks are made on an aluminum or glass substrate, on which a layer of ferromagnetic material is applied. The working layer mainly consists of iron oxide with various additives. The magnetic fields created by individual domains on a clean disk are randomly oriented and mutually compensate for any extended (macroscopic) area of the disk surface, so its remanent magnetization is zero.

If a portion of the disk surface is exposed to a magnetic field as it is pulled near the head gap, the domains align in a specific direction and their magnetic fields no longer cancel each other out. As a result, residual magnetization appears in this area, which can be subsequently detected. In scientific terms, we can say: the residual magnetic flux formed by a given area of the disk surface becomes nonzero.

Read / write head designs

With the development of technology for the production of disk drives, the designs of read / write heads have also improved. The first heads were wound cores (electromagnets). By modern standards, their dimensions were enormous, and the recording density was extremely low. Over the years, head designs have come a long way from the first heads with ferrite cores to modern types.

The most commonly used heads are of the following four types:

ü ferrite;

ü with metal in the gap (MIG);

ü thin-film (TF);

ü magnetoresistive (MR);

ü giant magnetoresistive (GMR).

· Ferrite heads

Classic ferrite heads were first used in IBM's Winchester 30-30 drive. Their cores are made on the basis of pressed ferrite (based on iron oxide). The magnetic field in the gap occurs when an electric current flows through the winding. In turn, with changes in the magnetic field strength near the gap in the winding, an electromotive force is induced. Thus, the head is versatile, i.e. can be used for both writing and reading. The dimensions and weight of ferrite heads are larger than those of thin-film ones; therefore, in order to prevent their unwanted contact with the surfaces of the discs, it is necessary to increase the gap.

During the existence of ferrite heads, their original (monolithic) design has been significantly improved. In particular, so-called glass-ferrite (composite) heads have been developed, a small ferrite core of which is installed in a ceramic body. The width of the core and the magnetic gap of such heads is smaller, which allows to increase the density of the recording tracks. In addition, their sensitivity to external magnetic interference is reduced.

· Heads with metal in the gap

Metal-In-Gap (MIG) heads are the result of improvements in the design of the composite ferrite head. In such heads, the magnetic gap located at the back of the core is filled with metal. Due to this, the tendency of the core material to magnetic saturation is significantly reduced, which makes it possible to increase the magnetic induction in the working gap and, therefore, to write to the disc with a higher density. In addition, the gradient of the magnetic field created by the head with the metal in the gap is higher, which means that magnetized areas with more pronounced boundaries are formed on the disk surface (the width of the sign reversal zones decreases).

These heads allow the use of media with a high coercive force and a thin-film working layer. By reducing the overall weight and improving the design, such heads can be located closer to the surface of the carrier.

Heads with metal in the gap are of two types: one-sided and two-sided (i.e. with one and two metallized gaps). In one-sided heads, a magnetic alloy interlayer is located only in the back (non-working) gap, and in two-sided heads, in both. A layer of metal is applied by vacuum deposition. The saturation induction of a magnetic alloy is approximately twice that of ferrite, which, as already noted, allows recording on media with a high coercive force, which are used in high-capacity drives. Reversible heads are better than unilateral ones in this respect.

· Thin film heads

Thin Film (TF) heads are manufactured using almost the same technology as integrated circuits, i.e. by photolithography. Several thousand heads can be "printed" on one substrate at once, which are small and light as a result.

The working gap in thin-film heads can be made very narrow, and its width is adjusted during production by building up additional layers of non-magnetic aluminum alloy. Aluminum completely fills the working gap and protects it well from damage (edge chipping) in case of accidental contact with the disc. The core itself is made of an alloy of iron and nickel, the saturation induction of which is 2–4 times higher than that of ferrite.

The areas of remanent magnetization formed by the thin-film heads on the disk surface have clearly defined boundaries, which makes it possible to achieve a very high recording density. Due to the light weight and small dimensions of the heads, it is possible to significantly reduce the gap between them and the surfaces of the disks in comparison with ferrite and MIG heads: in some drives, its value does not exceed 0.05 microns. As a result, firstly, the remanent magnetization of the surface areas of the carrier increases and, secondly, the signal amplitude increases and the signal-to-noise ratio in the readout mode improves, which ultimately affects the reliability of data recording and reading.

Today, thin-film heads are used in most high-capacity drives, especially in small-sized models, practically displacing heads with metal in the gap. Their design and characteristics are constantly improving, but, most likely, in the near future they will be replaced by magnetoresistive heads.

· Magnetoresistive heads

Magneto-Resistive (MR) heads are relatively recent. They are developed by IBM and allow achieving the highest values of recording density and speed of storage devices. Magnetoresistive heads were first installed in an IBM 1GB (3.5 ") hard drive in 1991.

All heads are detectors, i.e. records changes in the magnetization zones and converts them into electrical signals that can be interpreted as data. However, there is one problem with magnetic recording: as the magnetic domains of the media decrease, the signal level of the head decreases and there is a possibility of mistaking the noise for the “real” signal. To solve this problem, it is necessary to have an effective reading head, which can more reliably determine the presence of a signal.

Magnetoresistive heads are more expensive and more complex than other types of heads, since there are additional elements in their design, and the technological process includes several additional stages. The following are the main differences between magnetoresistive heads and conventional heads:

v additional wires must be connected to them to supply the measuring current to the resistance sensor;

v 4–6 additional masks (photomasks) are used in the production process;

v Due to their high sensitivity, magnetoresistive heads are more susceptible to external magnetic fields, so they have to be carefully shielded.

In all the previously considered heads, the same gap “worked” in the process of writing and reading, and in the magnetoresistive head there are two of them, each for its own operation. When designing heads with one working gap, you have to make a compromise in the choice of its width. The fact is that to improve the parameters of the head in the readout mode, it is necessary to reduce the width of the gap (to increase the resolution), and during recording, the gap should be wider, since the magnetic flux penetrates into the working layer to a greater depth (“magnetizing” it throughout thickness). In magnetoresistive heads with two gaps, each of them can have an optimal width. Another feature of the heads under consideration is that their recording (thin-film) part forms wider tracks on the disk than is necessary for the operation of the reading unit (magnetoresistive). In this case, the read head “collects” less magnetic interference from adjacent tracks.

· Giant magnetoresistive heads

In 1997, IBM announced a new type of magnetoresistive head with much greater sensitivity. They were called Giant Magnetoresistive (GMR) heads. They got this name based on the effect used (although they were smaller in size than standard magnetoresistive heads). The GMR effect was discovered in 1988 in crystals placed in a very strong magnetic field (approximately 1,000 times the magnetic field used in hard disk drives).

Data encoding methods

Magnetic data is stored in analog form. At the same time, the data itself is presented in digital form, since it is a sequence of zeros and ones. When recording is performed, digital information arriving at the magnetic head creates magnetic domains of the corresponding polarity on the disk. If a positive signal arrives at the head during recording, the magnetic domains are polarized in one direction, and if negative, in the opposite direction. When the polarity of the recorded signal changes, the polarity of the magnetic domains also changes.

If, during playback, the head registers a group of magnetic domains of the same polarity, it does not generate any signals; lasing occurs only when the head detects a change in polarity. These moments of polarity reversal are called sign reversals. Each sign change causes the read head to emit a voltage pulse; it is these pulses that the device registers during data reading. But at the same time, the read head generates a signal that is not exactly the one that was written; in fact, it creates a series of impulses, each of which corresponds to the moment of the sign change.

To optimally position the pulses in the recording signal, the raw raw data is passed through a special device called an encoder / decoder. This device converts binary data into electrical signals that are optimized for the placement of sign reversal zones on the recording track. During reading, the encoder / decoder performs the inverse transformation: it reconstructs a sequence of binary data from the signal. Over the years, several methods of data encoding have been developed, with the main goal of the developers being to achieve maximum efficiency and reliability of recording and reading information.

When working with digital data, synchronization is of particular importance. During reading or writing, it is very important to accurately determine the moment of each sign change. If there is no synchronization, then the moment of the sign change can be determined incorrectly, as a result of which the loss or distortion of information is inevitable. To prevent this, the operation of the transmitting and receiving devices must be strictly synchronized. There are two ways to solve this problem. First, synchronize the operation of two devices by transmitting a special synchronization signal (or sync signal) over a separate communication channel. Second, combine the sync signal with the data signal and transmit them together over the same channel. This is the essence of most data encoding methods.

Although a great many of the most diverse methods have been developed, today only three of them are actually used:

ü frequency modulation (FM);

ü modified frequency modulation (MFM);

ü encoding with the limitation of the length of the record field (RLL).

Frequency Modulation (FM)

The FM (Frequency Modulation) coding method was developed before others and was used when recording to floppy disks of the so-called single density (single density) in early PCs. The capacity of these single-sided floppies was only 80KB. In the 1970s, FM recording was used in many devices, but has now been completely abandoned.

Modified frequency modulation (MFM)

The main goal of the developers of the MFM (Modified Frequency Modulation) method was to reduce the number of sign change zones for recording the same amount of data compared to FM coding and, accordingly, to increase the potential capacity of the carrier. With this recording method, the number of sign changing areas used only for synchronization is reduced. Synchronization transitions are written only at the beginning of cells with a zero data bit and only if it is preceded by a zero bit. In all other cases, the sync sign change zone is not formed. Due to such a decrease in the number of sign changing zones with the same permissible density of their placement on the disk, the information capacity is doubled in comparison with the recording by the FM method.

This is why MFM discs are often referred to as double density discs. Since with the considered recording method, the same number of sign-changing zones has twice as much “useful” data as with FM coding, the speed of reading and writing information to the medium is also doubled.

Record Field Length Constrained Encoding (RLL)

By far the most popular coding method is Run Length Limited (RLL). It allows you to place on a disc one and a half times more information than when recording using the MFM method, and three times more than when FM coding. When using this method, not individual bits are encoded, but whole groups, as a result of which certain sequences of sign changing zones are created.

The RLL method was developed by IBM and was first used in disk drives on large machines. In the late 1980s, it was used in hard disk drives in PCs, and today it is used in almost all PCs.

Measuring storage capacity

In December 1998, the International Electrotechnical Commission (IEC), an electrotechnical standardization standard, introduced a system of names and symbols for units of measurement for use in data processing and transmission as an official standard. Until recently, with the simultaneous use of decimal and binary measurement systems, one megabyte could be equal to both 1 million bytes (106) and 1,048,576 bytes (220). Standard abbreviations of units used to measure the capacity of magnetic and other storage devices are given in table. 1.

According to the new standard, 1 MiB (mebibyte) contains 220 (1,048,576) bytes, and 1 MB (megabyte) contains 106 (1,000,000) bytes. Unfortunately, there is no generally accepted way to distinguish binary multiples of units from decimal ones. In other words, the English abbreviation MB (or M) can stand for both millions of bytes and megabytes.

Typically, storage capacities are measured in binary units, but storage capacities are in both decimal and binary units, which often leads to confusion. Note also that in English, bits and Bytes differ in the case of the first letter (it can be uppercase or lowercase). For example, when referring to millions of bits, the lowercase letter “b” is used, resulting in the unit of measure for million bits per second being Mbps, while MBps means million bytes per second.

What is a hard drive

The most necessary and at the same time the most mysterious component of the computer is the hard disk drive. As you know, it is designed to store data, and the consequences of its failure are often catastrophic. To properly operate or upgrade your computer, you need to have a good idea of what it is - a hard disk drive.

The main elements of the storage are several round aluminum or non-crystalline glassy plates. Unlike floppy disks (floppy disks), they cannot be bent; hence the name hard disk appeared (Fig. 4). In most devices, they are non-removable, so sometimes these drives are called fixed (fixed disk). There are also removable drives such as Iomega Zip and Jaz devices.

Latest Achievements

In the nearly 20 years that have passed since the time when hard drives became common components of personal computers, their parameters have changed radically. To give some idea of how far the process of improving hard drives has come, here are some of the brightest facts.

Maximum capacities for 5.25 "drives have increased from 10MB (1982) to 180GB and more for half-height 3.5" drives (Seagate Barracuda 180). The capacity of 2.5-inch drives with a height of less than 12.5 mm, which are used in laptop computers, has grown to 32 GB (IBM Travelstar 32GH). Hard drives of less than 10 GB are hardly used in modern desktop computers.

Data transfer rates have increased from 85-102 KB / s in the IBM XT (1983) to 51.15 MB / s in the fastest systems (Seagate Cheetah 73LP).

The average seek time (i.e., the time to set the head to the desired track) has decreased from 85 ms in the IBM XT computer (1983) to 4.2 ms in one of the fastest disk drives available today (Seagate Cheetah X15).

In 1982, a 10MB drive cost over $ 1,500 ($ 150 per megabyte). Nowadays, the cost of hard drives has dropped to half a cent per megabyte.

Rice. 4. View of the hard drive with the top cover removed

How hard drives work

In hard drives, data is written and read by universal read / write heads from the surface of rotating magnetic disks, divided into tracks and sectors (512 bytes each), as shown in Fig. 5.

Drives usually have multiple disks and data is written on both sides of each. Most drives have at least two or three discs (allowing recording on four or six sides), but there are also drives with up to 11 or more discs. Tracks of the same type (equally located) on all sides of the discs are combined into a cylinder (Fig. 6). Each side of the disk has its own read / write track, but all the heads are mounted on a common rod, or rack. Therefore, the heads cannot move independently of each other and move only synchronously.

Hard drives spin much faster than floppy drives. Their rotational speed even in most of the first models was 3,600 rpm (i.e. 10 times more than in a floppy drive) and until recently was almost the standard for hard drives. But now the rotational speed of hard drives has increased. For example, in a Toshiba laptop, a 3.3 GB disk rotates at 4,852 rpm, but there are already models with frequencies of 5,400, 5,600, 6,400, 7,200, 10,000 and even 15,000 rpm. The speed of a particular hard disk depends on its rotation frequency, the speed of movement of the head system and the number of sectors on the track.

During normal operation of the hard disk, the read / write heads do not touch (and should not touch!) The disks. But when you turn off the power and stop the discs, they sink to the surface. During operation of the device, a very small air gap (air cushion) is formed between the head and the surface of the rotating disc. If a speck of dust gets into this gap or a shock occurs, the head will “collide” with the disc, which is rotating “at full speed”. If the blow is strong enough, the head will break. The consequences of this can be different - from the loss of several bytes of data to the failure of the entire drive. Therefore, in most drives, the surfaces of magnetic disks are alloyed and coated with special lubricants, which allows the devices to withstand the daily “ups” and “landings” of the heads, as well as more serious shocks.

Rice. 5. Tracks and sectors of the hard drive

Rice. 6. Drive cylinder

on hard drives

Tracks and sectors

A track is one “ring” of data on one side of the disc. The recording track on the disc is too large to be used as a storage unit. In many drives, its capacity exceeds 100 thousand bytes, and it is extremely wasteful to allocate such a block for storing a small file. Therefore, the tracks on the disc are divided into numbered sections called sectors.

The number of sectors can be different depending on the density of the tracks and the type of drive. For example, a floppy disk track can be from 8 to 36 sectors, and a hard disk track can be from 380 to 700. Sectors created using standard formatting programs have a capacity of 512 bytes, but it is possible that this value will change in the future.

Sectors on a track are numbered from one, unlike heads and cylinders, which are counted from zero. For example, a 3.5-inch HD (High Density) diskette (1.44 MB capacity) contains 80 cylinders numbered 0 to 79, the drive has two heads (numbered 0 and 1), and each cylinder track is split into 18 sectors (1-18).

When the disk is formatted at the beginning and end of each sector, additional areas are created to record their numbers, as well as other service information, thanks to which the controller identifies the beginning and end of the sector. This allows you to distinguish between unformatted and formatted disk capacities. After formatting, the disk capacity decreases, and you have to put up with this, because to ensure normal operation of the drive, some disk space must be reserved for service information.

At the beginning of each sector, its header (or prefix portion) is written, which determines the beginning and the sector number, and at the end, a conclusion (or suffix portion), which contains a checksum (checksum) required to verify the data integrity ... Most newer drives use a so-called No-ID record instead of a header, which can accommodate a larger amount of data. In addition to the indicated areas of service information, each sector contains a data area with a capacity of 512 bytes.

For clarity, imagine the sectors are pages in a book. Each page contains text, but it does not fill all the space on the page, since it has margins (top, bottom, right and left). Service information is placed on the margins, for example, the titles of chapters (in our analogy, this will correspond to the numbers of tracks and cylinders) and page numbers (which corresponds to the numbers of sectors). Areas on disk that are similar to fields on a page are created when the disk is formatted; then the service information is also recorded in them. In addition, during disk formatting, the data areas of each sector are filled with dummy values. After formatting the disc, you can write information in the data area as usual. The information contained in the sector headers and conclusions does not change during normal data write operations. You can change it only by reformatting the disk.

Formatting disks

There are two types of disk formatting:

ü physical, or low-level formatting;

ü logical, or high-level formatting.

When formatting floppy disks using Explorer Windows 9x or the DOS FORMAT command, both operations are performed, but must be performed separately for hard disks. Moreover, for a hard disk, there is a third stage, performed between the two specified formatting operations, - partitioning the disk into partitions. Partitioning is absolutely essential if you intend to use multiple operating systems on the same computer. Physical formatting is always done the same way, regardless of operating system properties and high-level formatting options (which may be different for different operating systems). This allows multiple operating systems to be combined on one hard drive.

When organizing several partitions on one drive, each of them can be used to operate under its own operating system, or represent a separate volume (volume), or a logical drive (logical drive). A volume, or logical drive, is what the system assigns a drive letter to.

Thus, formatting a hard drive is a three-step process.

1. Low-level formatting.

2. Organization of partitions on the disk.