External memory- this is a place for long-term storage of data not used in at the moment in the computer's RAM. External memory is non-volatile.

To work with external memory you must have drive and storage devices - carrier.

Main types of storage devices:

floppy magnetic disk drives (FMD);

hard magnetic disk drives (HDD);

magnetic tape drives (TMD);

CD-ROM, CD-RW, DVD drives.

A hard disk drive is a random access information storage device based on the principle of magnetic recording. It is the main data storage device in most computers.
Information in the HDD is recorded on rigid (aluminum or glass) plates

Floppy disk, flexible magnetic disk - a portable, removable storage medium used for repeated recording and storage of data. It is a disk placed in a protective plastic case. A floppy drive is used to read floppy disks. Floppy disks typically have a write-protect feature that allows read-only access to the data.

CD-ROM is a type of compact disc with read-only data recorded on it. CD-ROMs are a popular and cheapest means of distribution software, computer games, multimedia

And other data.

Flash memory is a type of semiconductor electrically reprogrammable memory technology. The same word is used in electronic circuitry to designate technologically complete solutions of permanent storage devices in the form of microcircuits based on this semiconductor technology. In everyday life, this phrase is assigned to a wide class of solid-state information storage devices.

A logical disk is a part of a computer's long-term memory designed to store information on a hard drive. Logical drives are used to organize data located on a hard drive and make it easier to work with information.

A “logical disk” is the opposite of a “physical disk,” which refers to the memory of any particular disk medium.

The entire hard drive can be a logical disk, but for the convenience of working with information, as well as to ensure greater security, hard drive usually divided into sections. It is recommended to leave a certain percentage of the total volume for the system partition hard drive. A hard drive is a physical device that you can see and touch with your hands. A logical disk simply does not exist physically; it is just one of the hard drive partitions.

External computer memory consists of disk storage devices - a built-in hard disk drive (hard drive) and a drive on removable floppy disks (floppy disks). In both cases, magnetic disks store information in the form of magnetized concentric tracks (cylinders) on a magnetic coating, divided into sectors. The disk in the drive is constantly rotating, and information is written and read by magnetic heads moving along the radius of the disk. Thanks to the constant progress of drive production technology, the development of magnetic coating technology and magnetic heads, the capacity of hard drives has increased to several tens of gigabytes, and the capacity of floppy disks to hundreds of megabytes (however, the floppy disk capacity of 1.44 MB is still considered standard).

A detailed description of the operation of disk drives and the principles of storing information on magnetic disks would require too much space, and besides, it is not directly related to the topic of this book, so we will present here only some of the features of organizing information exchange.

Important parameter of any drive is its performance, which is determined, on the one hand, by the achievable speed of writing/reading information, and on the other, by the time of positioning (that is, installation in the desired position) of the magnetic head of the drive. The speed of the interface that connects the computer to the drive, as well as the methods used to organize information exchange, are also important.

Currently, the two most common standard interfaces for hard drives are:

IDE (Integrated Drive Electronics)- interface for disk drives, official name is ATA (AT Attachment). It is this interface that is used as the main one in personal computers. The exchange speed can reach 133 MB/s.

SCSI (Small Computer System Interface)- small computer system interface. In principle, it is also used to connect other devices (for example, scanners), but its main use is for disk drives. As a rule, this interface initially included in the structure of only some servers, and for its implementation on personal computers it is necessary additional fee extensions (by the way, quite expensive). The exchange speed can reach 320 MB/s.

A comparison of these two interfaces (SCSI and IDE) shows that in single-user standalone systems it is much more efficient to use IDE, while in multi-user and multitasking systems SCSI becomes more profitable. It's also worth noting that SCSI installation is more complex and expensive than IDE. In addition, when using a hard drive with a SCSI interface as a network drive, problems may arise. The advantage of SCSI is a larger number of maximally connected disk drives and the ability for them to simultaneously execute commands. As for the exchange rate, it is mainly determined not throughput interface, but by other parameters, in particular the speed used system bus. Therefore, in the general case it is impossible to say exactly which drive with which interface will work faster. Moreover, in the case of IDE, the actual speed very much depends on the circuit design solutions used by the drive manufacturer.

To speed up exchanges with disks, caching is widely used, the principle of which is close to the principle of RAM caching. In the same way, disk caching allows, by using faster electronic memory than disk memory, to significantly increase the average speed of exchange with the disk. Several points are fundamentally important here:

In most cases, each subsequent access to the disk will be an access to the next block of information on the disk;

Positioning the head requires a noticeable amount of time (on the order of a millisecond);

The desired sector on the disk may not be under the head after it is installed, and you will need to wait for its arrival.

All this leads to the fact that it turns out to be much more profitable to keep a copy of part of the disk in RAM (disk cache memory) and access the disk only if the necessary information is not in the cache memory. To exchange with cache memory, as in the case of RAM, the Write Through (WT) and Write Back (WB) methods are used. Since the hard drive is block-

oriented device (block size is 512 bytes), then data is transferred to the cache in blocks. When the cache memory is full, not only the currently needed blocks are written into it, but also the ones following them (the Read Ahead method), which are most likely to be accessed later. Caching is especially effective when optimizing a hard drive (defragmenting it), when each file is located in a group of sectors following each other. Like memory caching, disk caching uses LRU to update blocks that have not been accessed the longest. Disk cache memory is usually located on a special disk drive cache controller board and can be up to 16 MB in size.

To pair a disk drive with a computer floppy disks(floppy disks, floppy disks) a special SA-400 interface, developed in the early 70s, is traditionally used. The controller is connected to the drive by a 34-wire cable, and up to two drives are usually connected to one controller (theoretically there can be four). Each drive usually has four jumpers DSO-DS3 (Drive Select) to select the number of a given drive. Data via the interface is transmitted in serial code in both directions (via different wires). The data transfer rate for 1.44 MB floppy disks is 500 Kbps. Like the hard drive controller, the floppy drive controller in modern computers is installed on system board(special expansion cards were produced for older computer models).

An optical compact disc drive (CD-ROM) has become standard in newer computers. On these disks, information is stored in the form of zones with different degrees of light reflection from the surface of the disk. Instead of many concentric tracks on the surface of the disk (like a magnetic disk, a hard drive), in the case of a CD, only one spiral track is used. A miniature laser is used to read information. The disks have a diameter of 5 inches and a standard capacity of 780 MB. The speed of information exchange with CDs now ranges from 2.4 MB/s (for 16x drives) to 3.6 MB/s (for 52x drives). IDE and SCSI interfaces are used. Not only data, but also sound and images are recorded on a CD. There are CDs with the ability to write once or even rewrite information from a computer multiple times. Perhaps drives that support such drives will soon become standard personal computer. True, the speed of writing information to CDs is usually significantly lower than the speed of reading information.

Storage media (floppy disks, hard disks, CD-ROMs, magnetic optical discs etc.) and their main characteristics.

External (long-term) memory is a place for long-term storage of data (programs, calculation results, texts, etc.) not currently used in the computer's RAM. External memory, unlike RAM, is non-volatile. Carriers external memory In addition, they provide data transportation in cases where computers are not connected to networks (local or global).

To work with external memory, you must have a drive (a device that provides recording and (or) reading of information) and a storage device - media.

Main types of storage devices:

floppy magnetic disk drives (FMD);

hard magnetic disk drives (HDD);

magnetic tape drives (TMD);

CD-ROM, CD-RW, DVD drives.

The main types of media correspond to them:

flexible magnetic disks (Floppy Disk) (diameter 3.5'' and capacity 1.44 MB; diameter 5.25'' and capacity 1.2 MB (currently obsolete and practically not used, production of drives designed for disks with a diameter 5.25'', also discontinued)), disks for removable media;

hard magnetic disks (Hard Disk);

cassettes for streamers and other NML;

CD-ROM, CD-R, CD-RW, DVD discs.

Storage devices are usually divided into types and categories in connection with their operating principles, operational, technical, physical, software and other characteristics. For example, according to the operating principles, the following types of devices are distinguished: electronic, magnetic, optical and mixed - magneto-optical. Each type of device is organized on the basis of the corresponding technology for storing/reproducing/recording digital information. Therefore, in connection with the type and technical design of the information carrier, they distinguish: electronic, disk and tape devices.

Main characteristics of drives and media:

information capacity;

speed of information exchange;

reliability of information storage;

price.

Let's take a closer look at the above drives and media.

The operating principle of magnetic storage devices is based on methods of storing information using the magnetic properties of materials. As a rule, magnetic storage devices consist of actual devices for reading/writing information and a magnetic medium on which information is directly recorded and from which information is read. Magnetic storage devices are usually divided into types in connection with their design, physical and technical characteristics of the storage medium, etc. The most common distinctions are made between disk and tape devices. The general technology of magnetic storage devices consists of magnetizing areas of the media with an alternating magnetic field and reading information encoded as areas of alternating magnetization. Disk media, as a rule, are magnetized along concentric fields - tracks located along the entire plane of the discoidal rotating media. The recording is made in a digital code. Magnetization is achieved by creating an alternating magnetic field using read/write heads. The heads are two or more magnetic controlled circuits with cores, the windings of which are supplied with alternating voltage. A change in voltage causes a change in the direction of the magnetic induction lines of the magnetic field and, when the carrier is magnetized, means a change in the value of the information bit from 1 to 0 or from 0 to 1.

Disk devices are divided into flexible (Floppy Disk) and hard (Hard Disk) drives and media. The main property of disk magnetic devices is the recording of information onto the media on concentric closed tracks using physical and logical digital encoding of information. The flat disk media rotates during the reading/writing process, which ensures servicing of the entire concentric track; reading and writing is carried out using magnetic read/write heads, which are positioned along the radius of the media from one track to another.

For the operating system, data on disks is organized into tracks and sectors. The tracks (40 or 80) are narrow concentric rings on the disk. Each track is divided into parts called sectors. When reading or writing, the device always reads or writes an integer number of sectors, regardless of the amount of information requested. The sector size on a floppy disk is 512 bytes. A cylinder is the total number of tracks from which information can be read without moving the heads. Because a floppy disk has only two sides and a floppy drive has only two heads, a floppy disk has two tracks per cylinder. A hard drive can have many platters, each with two (or more) heads, so one cylinder has many tracks. A cluster (or data location cell) is the smallest disk area that the operating system uses when writing a file. Typically a cluster is one or more sectors.

Before use, the floppy disk must be formatted, i.e. its logical and physical structure must be created.

Floppy disks 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 a radiator);

expose the floppy disk to magnetic fields.

Drives on hard drives combine in one case the media (media) and the read/write device, as well as, often, an interface part called the hard disk controller. A typical design of a hard drive is a single device - a chamber, inside of which there is one or more disk media placed on one axis, and a block of read/write heads with their common drive mechanism. Typically, next to the media and head chamber there are circuits for controlling the heads, disks and, often, an interface part and (or) a controller. The interface card of the device contains the disk device interface itself, and the controller with its interface is located on the device itself. The drive circuits are connected to the interface adapter using a set of cables.

The principle of operation of hard drives is similar to this principle for GMD.

Basic physical and logical parameters of the hard drive.

Disc diameter. The most common drives with disk diameters are 2.2, 2.3, 3.14 and 5.25 inches.

Number of surfaces - determines the number of physical disks strung on the axis.

Number of cylinders - determines how many tracks will be located on one surface.

Number of sectors - the total number of sectors on all tracks of all surfaces of the drive.

Number of sectors per track - the total number of sectors on one track. For modern drives, the indicator is conditional, because they have an unequal number of sectors on external and internal tracks, hidden from the system and the user by the device interface.

The transition time from one track to another is usually from 3.5 to 5 milliseconds, and the fastest models can be from 0.6 to 1 millisecond. This indicator is one of the factors that determines the performance of the drive, because... It is the transition from track to track that is the longest process in a series of random read/write processes on a disk device.

Setup time or seek time is the time spent by the device moving the read/write heads to the desired cylinder from an arbitrary position.

The data transfer rate, also called throughput, determines the speed at which data is read or written to the disk once the heads are in position. Measured in megabytes per second (MBps) or megabits per second (Mbps) and is a characteristic of the controller and interface.

Currently, hard drives with capacities ranging from 10 GB to 80 GB are mainly used. The most popular are disks with a capacity of 20, 30, 40 GB.

In addition to NGMD and NGMD, removable media are often used. A fairly popular storage device is Zip. It is available as integrated or stand-alone units connected to a parallel port. These drives can store 100 and 250 MB of data on cartridges resembling a 3.5” floppy disk, provide an access time of 29 ms and data transfer speeds of up to 1 MB/s. If a device is connected to the system via a parallel port, then the data transfer rate is limited by the speed of the parallel port.

The Jaz drive is a type of removable hard disk drive. The capacity of the cartridge used is 1 or 2 GB. The disadvantage is the high cost of the cartridge. The main application is data backup.

In magnetic tape drives (most often such devices are streamers), recording is done on mini-cassettes. The capacity of such cassettes is from 40 MB to 13 GB, the data transfer speed is from 2 to 9 MB per minute, the tape length is from 63.5 to 230 m, the number of tracks is from 20 to 144.

CD-ROM is a read-only optical storage medium that can store up to 650 MB of data. Data on a CD-ROM is accessed faster than data on floppy disks, but slower than on hard drives.

The CD has a diameter of 120 mm (approx. 4.75'') and is made of polymer and covered with a metal film. Information is read from this metal film, which is coated with a polymer that protects the data from damage. CD-ROM is a one-way storage medium.

Reading information from the disk occurs by recording changes in the intensity of low-power laser radiation reflected from the aluminum layer. The receiver or photosensor determines whether the beam is reflected from a smooth surface, scattered, or absorbed. Scattering or absorption of the beam occurs in places where indentations were made during the recording process. The photo sensor perceives the scattered beam, and this information in the form of electrical signals is sent to a microprocessor, which converts these signals into binary data or sound.

External memory (ERAM) is designed for long-term storage of programs and data, and the integrity of its contents does not depend on whether the computer is turned on or off. This type of memory has a large capacity and low speed. Unlike RAM, external memory does not have a direct connection with the processor. Information from the OSD to the processor and vice versa circulates approximately along the following chain:

The computer's external memory includes:

hard disk drives;

floppy disk drives;

CD drives;

magnetic tape drives (streamers);

Magnetic-optical disk drives;

Hard drive

Hard disk (hard magnetic disk drives, HDD) is a type of permanent memory. Unlike RAM, data stored on a hard drive is not lost when the computer is turned off, making the hard drive ideal for long-term storage of programs and data files, as well as most important programs operating system. This ability (keeping information intact and safe after shutdown) allows you to remove a hard drive from one computer and insert it into another.

When turned on computer BIOS performs POST (power-on self-test) and checks whether there is a floppy disk in the drive. If there isn't one, it goes to the hard drive and copies a short program called "boot memory" from the hard drive to RAM. It then transfers control of the computer to a boot program, which oversees the loading of the operating system. Once the system is booted, the boot program is erased from memory, transferring control of the computer to the fully loaded operating system.

Hard drives are very reliable for storing large amounts of information and data. Inside a sealed hard drive are one or more inflexible disks coated with metal particles. Each disk has a head (a small electromagnet) built into an articulated arm that moves over the disk as it rotates. The head magnetizes the metal particles, causing them to line up to represent the zeros and ones of binary numbers. The motors that move the disc and lever are usually subject to wear and tear. Only the head can avoid wear, since it never comes into contact with the surface of the disc.

Another function of a hard drive is RAM simulation. Using hard drive sections as virtual memory Windows can run more programs. The disadvantage of virtual memory is that it is slow compared to regular memory. If you set more, your computer will slow down.

The hard drive, or hard drive, is the most important component of a computer. It stores the operating system, programs and data. Without operating room Windows systems You can’t start the computer, and without programs you can’t do anything once it’s already booted. Without a data bank, you will have to enter information manually each time.

The hard drive is a mechanical device in the computer and can cause more problems than electronic devices. It's actually very reliable. The discs are collected in clean rooms in which the air is constantly filtered and dust particles are removed. Hard drives are assembled from magnetically sensitive material. Before the discs are taken out of the room, they are packaged and sealed. If you open your hard drive out of curiosity, you can say goodbye to it. To prevent this from happening, never do this - you cannot open them.

New hard drives must be formatted before use. This process consists of laying magnetic concentric paths and breaking them into small sectors, like pieces in a cake. Be careful: if data was written to the hard drive, formatting it will completely destroy it.

Due to the much larger number of tracks on each side of the disks and the large number of disks, the information capacity of a hard disk can be hundreds of thousands of times greater than the information capacity of a floppy disk and reach 150-200 GB. The speed of writing and reading information from hard drives is quite high (can reach 133 MB/s) due to the fast rotation of the disks (up to 7200 rpm).

Hard drives use rather fragile and miniature elements (media platters, magnetic heads, etc.), therefore, in order to preserve information and performance, hard drives must be protected from shocks and sudden changes in spatial orientation during operation.

Floppy disk drives

Disk drives (floppy disk drives (FDD)) come in two main types - for large floppy disks (5.25 inches in size, sometimes written 5.25"), and for small ones (3.5 inches, 3. 5"). A five-inch floppy disk can hold, depending on its type, from 360 information (360 thousand characters) to 1.2 MB. Three-inch cards, although smaller, hold more information (720 KB - 1.44 MB). In addition, the three-inchers are enclosed in a plastic case, and therefore are more difficult to break or dent. Standard drive for modern computers is a drive for small (3.5-inch) floppy disks. Hence its name in a computer system - 3.5 A drive.

The 5-inch drive is located on system unit computer on the front and looks like a slot with a latch lever into which the floppy disk is inserted and latched. The 3-inch drive has a smaller slot (by 2 inches), and instead of a latch it has a button.

A floppy drive is more similar to a magnetic tape drive than a hard drive. Its head physically contacts the floppy disk and thus magnetizes the surface, protected from dust by a moving flap that automatically retracts when the disk is inserted into the drive.

Floppy drives supply data to the system through a cable connected to a connector on motherboard. It is different from the IDE controller used for hard drives and the data transfer speed is much slower.

Floppy disk drives are becoming little used, but still necessary. They are used only for transferring small amounts of data from one computer to another, as well as for emergency startup of a computer. CD-ROM drives are the primary method for distributing new software, but they are not required by the computer to perform data processing functions.

Flexible magnetic disks. Two main types

floppy disk floppy disk) or floppy disk, is a carrier of a small amount of information, which is a flexible plastic disk in a protective (plastic) shell. Used to transfer data from one computer to another and to distribute software.

In the center of the floppy disk there is a device for gripping and rotating the disk inside the plastic case. The floppy disk is inserted into the disk drive, which rotates the disk at a constant angular speed.

In this case, the magnetic head of the disk drive is installed on a certain concentric track of the disk, onto which information is written or from which information is read. The information capacity of a modern floppy disk is small and amounts to only 1.44 MB. The speed of writing and reading information is also low (only about 50 KB/s) due to the slow rotation of the disk (360 rpm).

In order to preserve information, floppy disks must be protected from exposure to strong magnetic fields (for example, do not place them next to a floppy disk mobile phone) and heating, since such physical effects can lead to demagnetization of the media and loss of information.

Currently, the most widespread are floppy disks with the following characteristics: diameter 3.5 inches (89 mm), capacity 1.44 MB, number of tracks 80, number of sectors on tracks 18 (Floppy disks with a diameter of 5.25" are now used very rarely, so their capacity does not exceed 1.2 MB, and besides, they are made of less durable material). spins up to a rotation speed of 360 per minute. The diskette itself rotates in the drive, the magnetic heads remain stationary only when it is accessed.

IN lately Three-inch floppy disks appeared that could store up to 3 GB of information. They are manufactured according to new technology Nano2 and require special hardware for reading and writing, which is not yet included in the standard package when purchasing a PC.

Floppy disk device

Floppy disks vary in size and capacity. By size, the division is made into floppy disks with a diameter of 5.25" (" - inch sign) and floppy disks with a diameter of 3.5". In terms of capacity - on double density floppy disks (in English double density, abbreviation - DD) and high density(high density, abbreviated as HD).

A 5.25" floppy disk consists of a protective plastic sleeve containing a magnetically coated plastic disk. This disk is thin and bends easily - that's why floppy disks are called floppy disks. Of course, you cannot bend the floppy disk, and this is prevented by the protective sleeve. The floppy disk has two holes - a large one in the center and a small one next to it. The large hole is designed to allow the magnetic disk to rotate inside the envelope.

This is done by a motor inside the drive. The inside of the protective envelope is covered with lint, which collects dust from the magnetic disk as it rotates. The small hole is used to count the revolutions of the disk inside the drive. The envelope has a longitudinal slot on both sides through which a disk with a magnetic coating is visible. Through this slot, a magnetic head inside the drive touches the disk and writes or reads data from it. Data is written to both sides of the disk. Never touch the surface of the magnetic disk with your fingers! By doing this, you can ruin it by scratching or greasy. If you turn the floppy disk with the slot facing you, with the label facing up, you will see a small rectangular cutout on the top right side of the envelope. If you cover it with pieces of sticky paper (usually sold with floppy disks), the disk will be write-protected. Typically, this cutout should be free; it should only be sealed on floppy disks with important data.

The structure of a 3.5" floppy disk is slightly different. Its protective sleeve is made of hard plastic, so such a floppy disk is more difficult to bend or break. The magnetic disk is not visible, since there are no open holes. There is a slot for access of the magnetic head to the surface of the disk, but it is covered with a latch. The latch is held closed by a spring. You do not need to open it with your hands to avoid damaging the magnetic disk. Inside the drive, the latch opens automatically. For write protection, the floppy disk has a small latch on the top left of the floppy disk if you hold the floppy disk with the large latch facing you. , with the label facing down. The down position for the write latch is normal, in this state the floppy disk is not write protected. To prevent data from being written to the floppy disk, slide the latch upward, which will open a small square hole in the diskette.

Floppy disk recording method

The method of recording binary information on a magnetic medium is called magnetic coding. It lies in the fact that magnetic domains in the medium are aligned along paths in the direction of the applied magnetic field with their north and south poles. Usually there is a one-to-one correspondence between binary information and orientation of magnetic domains.

Information is recorded along concentric tracks (tracks), which are divided into sectors. The number of tracks and sectors depends on the type and format of the floppy disk. A sector stores the minimum amount of information that can be written to or read from disk. The sector capacity is constant and amounts to 512 bytes.

A CD-ROM writer can record any type of information - music, images or text. There are recordable discs on which you can write information only once (CD-R). But there are also rewritable discs (CD-RW), they are more expensive, but they allow you to erase information and add new information. However, if you burn music to a rewritable CD, you can only listen to it on a PC, but the rewritable disc can be played on any CD player.

Optical principle of recording and reading information.

Laser CD-ROM and DVD-ROM drives use the optical principle of recording and reading information.

In the process of recording information on laser discs, various technologies are used to create surface areas with different reflectance coefficients: from simple stamping to changing the reflectivity of areas of the disc surface using a powerful laser. Information on a laser disk is recorded on one spiral-shaped track (like on a gramophone record), containing alternating sections with different reflectivity.

In the process of reading information from laser disks, a laser beam installed in the disk drive falls on the surface of the rotating disk and is reflected. Since the surface of the laser disk has areas with different reflection coefficients, the reflected beam also changes its intensity (logical 0 or 1). Then the reflected light pulses are converted using photocells into electrical pulses and transmitted via the highway to the RAM.

Subject to the rules of storage (in cases in an upright position) and operation (without causing scratches or contamination) optical media can retain information for decades.

Laser drives and disks

Laser drives (CD-ROM and DVD-ROM) use the optical principle of reading information.

Laser CD-ROM (CD - Compact Disk) and DVD-ROM (DVD - Digital Video Disk) disks store information that was recorded on them during the manufacturing process. It is impossible to write new information to them, which is reflected in the second part of their names: ROM (Real Only Memory - read only). Such discs are produced by stamping and have a silver color.

The information capacity of a CD-ROM disk can reach 650-700 MB, and the speed of reading information in a CD-ROM drive depends on the rotation speed of the disk. The first CD-ROM drives were single-speed and provided information reading speeds of 150 KB/s. Currently, 52-speed CD-ROM drives are widely used, which provide 52 times faster information reading speed (up to 7.8 MB/s).

DVDs have a much larger information capacity (up to 17 GB) compared to CDs. First, lasers with shorter wavelengths are used, which allows the optical tracks to be placed more densely. Secondly, information on DVDs can be recorded on two sides, with two layers on one side.

The first generation of DVD-ROM drives provided information reading speeds of approximately 1.3 MB/s. Currently, 16-speed DVD-ROM drives achieve read speeds of up to 21 MB/s.

There are CD-R and DVD-R discs (R - recordable) that are golden in color. Information on such disks can be written, but only once. On CD-RW and DVD-RW (RW - ReWritable) discs, which have a "platinum" tint, information can be recorded many times.

For recording and rewriting onto discs, special CD-RW and DVD-RW drives are used, which have a fairly powerful laser that allows you to change the reflectivity of surface areas during the recording process. These drives allow you to write and read information from disks at different speeds. For example, marking a CD-RW drive “40x12x48” means that CD-R discs are written at 40x speed, CD-RW discs are written at 12x speed, and CD-RW discs are read at 48x speed.

Magnetic tape drives (streamers) and removable disk drives

Streamer (English tape streamer) - a device for backup large amounts of information. The media used here are magnetic tape cassettes with a capacity of 1 - 2 GB or more.

Streamers allow you to record a huge amount of information onto a small magnetic tape cassette. The hardware compression tools built into the tape drive allow you to automatically compress information before recording it and restore it after reading it, which increases the amount of stored information.

The disadvantage of streamers is their relatively low speed of recording, searching and reading information. At the moment, streamers are outdated and therefore they are used very rarely in practice.

Recently, storage devices on removable disks have become increasingly used, which allows not only to increase the amount of stored information, but also to transfer information between computers. The volume of removable disks ranges from hundreds of MB to several gigabytes.

On this page we will talk about topics such as: , External computer memory, Magnetic storage, Hard drives, Winchester.

External computer memory, External storage devices.

External computer memory or VSD is an important component of an electronic computer that provides long-term storage of programs and data on various storage media. External storage devices(VZU) - can be classified according to a number of characteristics: by type of media, by type of design, by the principle of recording and reading information, by access method, etc. At the same time, under carrier refers to a material object capable of storing information.

External memory properties:

• The VRAM is non-volatile; the integrity of its contents does not depend on whether the computer is turned on or off.
• Unlike RAM, external memory has no direct connection with the processor.

The external memory includes:

• HDD – hard disk drives.
• NGMD – floppy disk drives.
• GCD – optical drives(CD-R, CD-RW, DVD).
• NML – magnetic tape drives(streamers).
• Memory cards.

Drives- This storage devices, designed for long-term (that is, independent of power supply) storage of large volumes of information.

In addition to its main characteristic - information capacity - disk drives are characterized by two other indicators: access time and speed of reading sequential bytes.

Hard disk drives.

Hard disk drive (HDD – Hard Disk Drive, hard drive) is a high-capacity storage device in which the information carriers are round aluminum plates, both surfaces of which are coated with a layer of magnetic material. Used for permanent storage of information - programs and data. HDD usually called "Winchester"- that’s how one of the first models began to be called at one time Hard disk drives, which had the designation “30/30” and thus resembled the markings of famous weapons.

Note

It is also possible that the name comes from the place of initial development - a branch of IBM in Winchester (UK), where the technology for creating hard drives…

Winchester.

The surface of a disk is treated as a series of dot positions, each of which is considered a bit and can be set to 0 or 1. Since the locations of dot positions are not precisely determined, recording requires pre-applied marks to help the recording device locate the recording positions. The process of applying such marks is called physical formatting and is required before using the drive for the first time. Winchesters have a very large capacity: from hundreds of megabytes (the oldest) to tens of terabytes.

Structural elements of a hard drive.

Thin concentric circles are marked on each side of each plate (synchronizing marks are located along them). Each concentric circle is called a track. Groups of paths (tracks) of the same radius located on the surfaces of magnetic disks are called cylinders.
The number of the cylinder coincides with the number of the forming track. HDD may have several tens of thousands of cylinders.

Each track is divided into sectors. A sector is the smallest addressable unit of data exchange between a disk device and RAM. Sector numbering starts from 1. In order for the disk controller to find the desired sector on the disk, it is necessary to give it all the components of the sector address: cylinder number, surface number, sector number ().

operating system When working with a disk, it usually uses its own unit of disk space, called a cluster. Cluster (data storage cell) is the amount of disk space involved in a single read/write operation performed by the operating system.

Magnetic storage devices.

Floppy disk drive — floppy disk, diskette(English) floppy disk) – a device for storing small amounts of information, which is a flexible plastic disk in a protective shell. The most common are “three-inch floppy disks.” A 3.5 floppy disk has 2 working surfaces, 80 tracks on each side, 18 sectors on each track (512 bytes per sector).

Floppy disk device: The principle of recording on magnetic media based on the magnetization of individual sections of the magnetic layer of the carrier. Information is recorded along concentric tracks (tracks), which are divided into sectors. The number of tracks and sectors depends on the type and format of the floppy disk. A sector stores the minimum amount of information that can be written to or read from disk. The sector capacity is constant and amounts to 512 bytes.

Note

Today, floppy disks are outdated, they have been replaced by more reliable, faster and more capacious media - optical disks and memory cards...

Magnetic tape drives (streamers).

Streamer (English tape streamer)– a device for backing up large amounts of information. As carrier Magnetic tape cassettes with a capacity of 1 - 2 GB or more are used here. The disadvantage of streamers is their relatively low speed of recording, searching and reading information.

Note

Today, streamers are outdated and practically not used...

This is where I end this article, I hope you have fully understood the topics: External storage devices, External computer memory, Magnetic storage, Hard drives, Winchester.