Hard drive and other types of external memory. External memory

External memory, sometimes called backup storage or secondary memory, allows you to store large amounts of information. Nowadays, external memory capacity is high, usually measured in hundreds of megabytes or even gigabytes (billion bytes). External memory has an important property: information is stored and not lost when the computer's power is turned off.

External memory (ERAM) is designed for long-term storage of programs, calculation results, texts, regardless of whether the computer is on or off. Unlike RAM, external memory does not have a direct connection with the processor. This is non-volatile memory.

Which includes:

HDD: hard magnetic disk drives;

FHD: floppy disk drives;

CD-ROM, CD-RW, DVD: compact disc drives;

Magneto-optical CD drives;

NML: magnetic tape drives (streamers).

The main task of the external memory of a personal computer is the ability to long-term store a sufficiently large amount of information (programs, texts, photographs, audio and video clips). A device that provides recording/reading of information is called a drive, or disk drive, and information is stored on media (for example, floppy disks).

Figure 3 - Classification of VZU

A floppy disk is the earliest type of information storage device that contains a small amount of data. They were invented in 1967 by a group of IBM specialists, designed to distribute software, read/write/transfer data from one PC to another.

It is a flexible plastic disk in a protective shell of a personal computer. The main components of a floppy disk are a magnetic disk that stores information and an envelope that performs a protective function for the disk.

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. Typically, a one-to-one correspondence is established between binary information and the 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.

Magnetic tape was designed to store data for 50 years. When storing large enough volumes of information, it was significantly cheaper to use tape than disk or other data storage options. Modern use of tape media is primarily associated with high average power for backup and archival purposes.

Figure 4 - Magnetic tape.

Writing and retrieving data is quite slow. Because magnetic tape uses sequential access for reading and writing. It is used for applications that require large memory capacity, where access speed is not an issue. Also widely used for backing up computer network file servers in a variety of batch processing applications, such as reading bank checks, payroll, and general stock control.

The most common form of external memory is a hard drive, which is permanently installed in the computer and typically has a capacity of hundreds of megabytes. Information is written to the disk by magnetizing the oxide coating on concentric circular tracks. This means that the correct path must be set before accessing or modifying read/write head data.

The hard drive contains all the software needed to run the computer. All user data and programs can also be stored on the hard drive. Additionally, most computers have some form of removable storage devices that can be used to save a copy of important files.

Like a floppy disk, the working surfaces of platters are divided into circular concentric tracks, and the tracks into sectors. The read-write heads, along with their supporting structure and disks, are enclosed in a hermetically sealed housing called a data module. When a data module is installed on a disk drive, it automatically connects to a system that pumps purified cooled air. The surface of the platter has a magnetic coating only 1.1 microns thick, as well as a layer of lubricant to protect the head from damage when lowering and raising on the go. When the platter rotates, an air layer is formed above it, which provides an air cushion for the head to hover at a height of 0.5 microns above the disk surface.

Optical disk drives use a disk coated with a reflective substance with special optical properties as the storage medium.

The most common types of optical media are Blu-Ray , CDs And DVDs. Computers can read and write to CDs and DVDs, use CD burners or DVD Writer and Blu-ray discs to read Blu-ray discs.

There are three main types of optical media: CDs, DVDs, and Blu-ray discs. CDs can store up to 700 megabytes (MB) of data and DVDs can store up to 8.4 GB of data. Blu-Ray discs, which are the newest types of optical media, can store up to 50 GB of data. This amount of memory is a clear advantage over (magnetic media), which has a capacity of 1.44 MB. Another advantage is that optical media has a more flexible disk, it can last up to 7 times longer due to its durability.

A standard CD consists of a base, reflective and protective layers. The base is made of transparent polycarbonate, on which an information relief is formed by pressing. A metal reflective layer is sprayed over the relief. The reflective layer is covered with a protective layer of varnish on top - so that the entire metal surface is protected from contact with the external environment.

Information is recorded on the disk in the form of a spiral track running from the center to the edge of the disk, on which indentations (the so-called pits) are located. The laser beam of the drive head passes along the track and reads information based on the nature of the reflected beam.

A USB (Universal Serial Bus) flash drive is a small, portable device that connects to a computer's USB port. Like a hard drive, it stores information, but is typically much smaller than most hard drives. USB flash drives vary in size and shape and contain gigabytes of information. They are sometimes called flash drives because they are the size and shape of a human finger. The main advantage is that flash drives can be easily carried, making it extremely convenient for transferring information from one computer to another.

memory hard drive storage media

Figure 5 - USB flash drive.

External data storage devices somehow unexpectedly entered our lives. You could say it was a leap. Currently, people highly value the mobility of information, as well as the speed of its transmission. That is why an external drive is a very valuable device that allows you to quickly exchange movies, games and other files (it should be noted, even of considerable size) between two computer devices.

General information

The question that arose in connection with the problem of storing user data, as well as accessing it, is quite relevant. This problem is very acute in families where everyone tries to carve out as much space on the computer as possible specifically for their needs. And an external drive can easily become a solution to such problems.

The optimal solution at present is, of course, various network storage systems, which in many companies are located directly inside buildings. In general, they have quite a lot of advantages. Previously, creating network storage required purchasing a separate computer that would play this role. Now, with the development of wireless technologies, this is no longer necessary. All you have to do is plug in your wireless router and the problem is solved.

Modern models are available with support for USB version 3.0 ports. And this also has weight, since the functionality is significantly expanded. What is even better than a network resource located at home, which, if necessary, can be taken with you on a trip? And this device will have such mobile dimensions that it will not burden absolutely anyone with its carrying!

In general, an external USB drive will be a solution to several problems at once. Models of external hard drives differ in their characteristics, and in this article we will analyze several devices, get acquainted with them in general and in general, and understand what advantages and disadvantages they have. This is done so that anyone can then go to the store and, based on the material they have read, if necessary, choose an external drive model for themselves.

So, many hard drives now have interesting, innovative interfaces. We are talking about USB 3.0 ports. They also have a large form factor. Next we will talk about whether it makes sense to purchase such disks, which are quite large in size and require power from an external source.

ADATA HD 710

This external memory drive is available in different versions, which differ in the amount of built-in memory. We are talking about allocating 500 gigabytes, 1 terabyte, and 2 terabytes. 500 GB, in our opinion, is now not enough for active use of the hard drive. But 1, and even more so 2 TB will be an excellent solution.

This external drive is available in three colors. The following colors are available: blue, yellow, black. All hard drives belonging to this series have a shockproof and waterproof casing. You can place the USB cable without any problems in the groove that was specially secured around the disk enclosure. Thus, the device developers solved the problem of convenient cable storage. Its length is about 30 centimeters. To be more precise, 31. The dimensions are quite average: with a weight of 220 grams, this external USB 3.0 drive has dimensions of 132 by 99 by 22 millimeters.

Hard drive. External hard drive HGST Touro Mobile MX3

This model, like its predecessor, has three modifications, equipped with different amounts of built-in long-term memory. We are talking about variations with a capacity of 500 gigabytes, as well as models with a capacity of 1 TB and 1.5 TB.

Among the shortcomings, it is worth noting the lack of legs that could combat the vibration of the hard drive during its operation. But the use of matte plastic as a housing material cannot be definitely considered. The USB cable doesn't fit anywhere. It has a length of 43 centimeters. This external hard drive is 126 millimeters long, 80 millimeters wide, and 15 millimeters high.

Seagate Expansion Portable

All Seagate models that belong to the Expansion series of portable external hard drives have the same form factor. It is equal to 2.5''. The model range of the series has three memory drives, which have corresponding volumes. This, according to the standard, is 500 gigabytes, 1 and 2 TB.

Like the model we reviewed earlier, the Seagate Expansion Portable does not have rubber feet. The housing of the series devices is made of matte plastic. These external storage devices have a USB cable 44 centimeters long. Dimensions of the hard drive are 122.3 millimeters in length, 81.1 millimeters in width, 15.5 millimeters in height. The mass of the drive is 170 grams.

Seagate Expansion

Models in this series differ from their predecessors not only in memory capacity, but also in their large form factor. It is 3.5''. Thus, the models automatically increase in size, weight, and also require an additional power source. The case of such hard drives is made of the same matte plastic. To combat the vibration that occurs during operation of the device, there are four rubber feet on its bottom. In the model range of this series you can see external hard drives with built-in memory capacity of 1, 2, 3, 4 and 5 terabytes.

The USB 3.0 cable is 118 centimeters long. A special power adapter is required for the hard drive to operate. It operates at a voltage of 12 volts and a current of 1.5 amperes. The length of such a drive reaches 179.5 millimeters. The width is 118 millimeters, and its height is 37.5 mm. In this case, the mass of the drive is 940 grams.

Silicon Power Armor A80

External drives of this series have a good casing, protected from moisture penetration, as well as from mechanical damage. The outer surface of the hard drive is made of anodized matte aluminum. To counter the vibration that occurs when working with the drive, there are no rubber feet.

The lineup consists of drives with three different memory capacities. These are 1 and 2 terabytes, as well as 500 gigabytes. The models in the series are slightly different from all the external drives that we have reviewed before. The fact is that they have two cables at once, which are designed to synchronize the device with a personal computer or laptop. The first cable is 79 centimeters long. The second one is 70 cm shorter. The case has an end where you can hide a short wire. Also, the hard drives of the series use a USB 3.0 A socket. All models that were described earlier use USB 3.0 Micro-B. Weighing 270 grams, the series hard drives measure 139.45 mm by 94 mm by 18.1 mm.

TOSHIBA Stor.E Basics

The body of this line of external memory drives is made of matte black plastic. There are four legs at the bottom of the gadget, which is good news. But as far as volume is concerned, the series may not please all users. The maximum amount of long-term memory available in such drives is 1 terabyte. The remaining two modifications of the series have capacities of 500 GB and 750 GB, respectively.

The USB 3.0 cable is not short, but not long either. Its length is 52.5 centimeters. It is interesting that the models in the series differ in size. The hard drive version, which has a capacity of 1 TB, weighs 180 grams and is 16.5 centimeters thick. At the same time, the remaining models will be thinner and lighter in terms of weight: their height is only 13.5 millimeters and their weight is 150 grams.

Transcend StoreJet 25H3

External drives of this brand have a casing that is covered with a rubber layer. Thus, the manufacturer took care of mechanical strength, adapting external hard drives of this series to unexpected mechanical shocks and loads. Models produced in the line have a memory capacity of 500 gigabytes, as well as 1 and 2 TB. If we talk about the color scheme, the hard drives of the series are available in purple and black, as well as in blue. The length of the cable for synchronization with a PC is about 45 centimeters.

A distinctive feature of this model range is that there is a button on the case that serves for quick reconnection. It helps activate a special mode. In this case, there is no need to disconnect and turn off the hard drive, and then synchronize it with the computer again. With a weight of 216 grams, the 500 GB and 1 TB versions of the drive have the following dimensions: length - 131.8 mm, width - 80.8 mm, and thickness - 19 millimeters. The model, which is designed for 2 terabytes of internal memory, is slightly thicker (24.5 mm) and weighs a little more (284 grams).

Western Digital My Passport Ultra

Like almost all other models, the serial range of this external hard memory drive is made of matte black plastic. There are four feet at the bottom that will save the device from vibration during operation. The hard drive cover, depending on its modification, may be of different colors. Currently available in black, blue, red and metallic.

The amount of built-in memory is standard: 500 gigabytes, 1 TB or 2 TB. The USB cable does not fold anywhere, its length is 46 centimeters. A special bag made of velvet is provided for transportation. Weight (depending on the model) varies from 130 to 230 grams. Overall dimensions also vary. The length can be from 110 to 110.5 millimeters, the width - from 81.6 to 82 millimeters. This is not so noticeable, but how the thickness of the hard drive increases with its memory capacity is visible quite clearly. It falls in the range from 12.8 to 20.9 millimeters.

Storage media (floppy disks, hard disks, CD-ROM disks, magneto-optical disks, 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. External memory media, in addition, provide data transportation in cases where computers are not networked (local or global).

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

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 a medium 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.

Hard disk drives combine the media(s) and the read/write device, and often also an interface part called the hard drive controller, into one housing. 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, 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.

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 reading speed of 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 ().

When working with a disk, the operating system 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.

The computer's external memory includes:

1) magnetic disk drives. Their work is based on the principle of magnetic recording (assuming that magnetic dipoles of the ferromagnetic layer preserve the direction of the acting external magnetic field) of data:

On removable flexible magnetic disks - NGMD (Floppy Disk Drive, FDD floppy disk, zip disk);

On hard magnetic disks such as Winchester HDD;

On removable hard drives;

2) storage devices on optical and magneto-optical CDs;

3) magnetic tape drives;

4) solid-state semiconductor memory.

1. Disk magnetic storage devices. Information on a disk coated with a layer of ferromagnetic substance is written and read using disk drives (drives) that have positionable read/write heads on one or both sides of the disk.

Floppy disks(English) floppy disk) are “veterans” among disk devices, since they were equipped with the first IBM PC models. Since then, disk drives have changed significantly and, despite the increased capacity, have ceased to be the main means of storing data and programs. Compared to other storage media, they have very low capacity and reliability, so they are used mainly for quickly transferring data from the hard drive of one computer to the hard drive of another, as well as creating archival copies.

Information on magnetic disks is written and read by magnetic heads along concentric circles - tracks (tracks). The number of tracks on a magnetic disk and their information capacity depend on the type of magnetic disk, drive design, quality of magnetic heads and magnetic coating. Each track of a magnetic disk is divided into sectors. Formation of tracks, sectors and recording of special marks , identifying primarily track numbers is provided by low-level marking (form-

matting). One track sector can accommodate 128,

256, 512 or 1024 bytes. Data exchange between the drive on the mag-

nit disk and RAM is carried out sequentially by an integer number of sectors. Cluster is the minimum unit of information placement on a disk, consisting of one or more adjacent sectors of a track (Figure 3.18).

Basic disk parameters:

1. Form factor. All disks: both magnetic and optical, are characterized by their diameter, or otherwise, form factor. Until now, disks with a form factor of 3.5" (89 mm) are used.

2. Recording density . All modern floppy disks and drives are double-sided, high density (marked - Double Sided High Density, DS/HD).

3. Full capacity. Disks with a 3.5" form factor have a capacity of 1.44 megabytes.

4. Access time and data reading speed in a row.

Figure 3.18 - Logical structure of the surface of a magnetic disk

The floppy disk is installed in floppy disk drive(floppy drive from English. floppy-disk drive), is automatically fixed in it, after which the drive mechanism spins up to a rotation speed of 360 min –1. The floppy disk itself rotates in the drive, the magnetic heads remain motionless. The floppy disk rotates only when it is accessed. The drive is connected to the processor through a floppy disk controller.

A number of companies produce floptic flexible disks - Very High Density disks. These are three-inch discs with a ferromagnetic layer applied using sophisticated technology. Up to 21 MB of data can be written to the disc. The disk contains up to 755 tracks, each of which has 27 standard-sized sectors. The disk rotation speed is about 720 rpm. The heads are positioned in the drive using a laser sensor. The exchange speed reaches 10 MB/s. Drives on such disks can be used to write and read information from standard three-inch floppy disks with a capacity of up to 1.44 MB.

Computer users are interested in storage devices on removable floppy disks - ZIP family drives with removable magnetic disks 3.5 inches with a capacity of 100-120 MB. ZIP models are available both internal and external. They rotate at a speed of 3000 rpm, have an average access time of about 29 ms, and provide data transfer at a speed of 790 kB/s (when using a standard LPT printer port) and 1.4 MB/s (for a built-in drive with a SCSI controller) . Current ZIP 750 drives are designed to work with media with a capacity of 750 MB. ZIP drives that implement LS-120 (Super Disk) technology read not only 120 MB disks, but also 1.44 MB floppy disks.

Zip drives are included as a standard drive in new computers from Apple, Compaq, Dell, Gateway2000, Hewlett-Packard, IBM, Packard Bell, etc. New models (including Zip Plus) are comparable in data reading speed to high-speed CD-ROM drives . The disadvantages of Zip include not the highest data transfer speed and incompatibility with floppy disks.

HiFD drives– allow you to save up to 200 MB of data on one removable magnetic disk (having the dimensions of a regular floppy disk). High data transfer speeds (up to 3.6 Mb/s) are achieved due to the angular rotation speed of the media equal to 3600 rpm and the use of high surface density of information recording. Like a hard disk drive, the head in HiFD technology floats above the surface of the platter, which significantly reduces wear on both the head and the media (Figure 3.19).

Figure 3.19 - Storage HiFD

jAZ drives– are similar to hard drives, but are replaceable. One disk can accommodate 1-2 GB. They use two 3.5-inch platters in an insulated cartridge. Among high-speed large-capacity storage devices, the leadership remains jAZ.

Disk arrays. To increase the capacity of external data storage devices with increased reliability, RAID drives are used. This is the combination of several disk drives into one high-capacity logical disk (hundreds of gigabytes). Such drives can be built into the computer case and placed in separate racks. RAID drives have increased data transfer speeds and reliability of data storage. The operation of the disk array is organized under the control of a RAID controller. The need to use RAID drives arises for workstations, multi-user servers and superservers.

Hard disk drive (HDD) Hard Disk Drive), or hard drive, is a storage device for long-term storage of large amounts of data and programs. This is not one disk, but a group of coaxial disks with a magnetic coating.

The information carriers here are round aluminum plates - platters, both surfaces of which are covered with a layer of magnetic material, that is, it has not 2 surfaces, but 2n, where n is the number of platters in the group. A simplified diagram of a hard drive is shown in Figure 3.20.

Figure 3.20 - Simplified hard drive diagram

The platter's magnetic coating is approximately 1.1 microns thick and also contains a layer of lubricant to protect the head from damage when lowering and raising while moving. Unlike a floppy disk, a hard disk rotates continuously. Since the rotation speed is quite high, an air cushion is formed between the magnetic surface and the read/write heads, and they float above the media (media) at a distance of 0.00005-0.0001 mm. The opinion that there is a vacuum inside the drive is erroneous, if only because where there is a vacuum, of course, there cannot be any air cushions. When the HDD is not working, the heads are located in a special landing zone ( Landing Zone), while they are blocked to avoid various damage to both the heads themselves and the media. When the engine is turned on, it spins the surfaces, and the heads come out of the landing zone under the influx of air.

The hard drive is connected to the processor via hard drive controller.

Recording and reading information are based on the principles that are used in ordinary household tape recorders. However, unlike magnetic recording on magnetic tape, recording on a hard (and floppy) disk is performed in separate blocks in separate sectors. Each sector, in addition to data, contains various service information necessary for the proper functioning of the drive controller. In particular, this service information includes data such as track number, sector number, and checksum of data recorded in the sector.

All modern drives are equipped with a built-in cache (usually 2 MB), which significantly increases their performance.

Hard drive characteristics:

1. Capacity. Currently, magnetic-resistive effect technology is used, where the theoretical capacity limit of 1 wafer is 20 GB, the technological level is 6.4 GB per wafer.

2. The speed of the hard drive is described by three parameters.

a) Data transfer rate (read/write speed) (transfer rate, briefly - transfer) shows how quickly data written strictly sequentially is read from the disk (measured in megabytes per second). For different disks, this value can vary greatly and ranges (at the time of writing) from approximately 15 MB/s to 60-100 MB/s. Moreover, decent disks should provide a transfer speed no worse than 30 MB/s, better than 40 MB/s (note that we are talking about the peak transfer speed, which is observed when working mainly with the first tracks of the disk and reading/writing entire data arrays, and in real conditions, when small portions are exchanged with the entire disk, the values will be almost an order of magnitude lower).

b) Average access time( average seek time, briefly - seek) is the average time during which the required data block will be found if the hard drive is given its physical location, measured in milliseconds. Access time can vary anywhere from 12-10 ms to 5-4 ms. Also, the disk characteristics usually mention the transition time to the adjacent track, which, as a rule, is about 1.5-0.5 ms (good disks have no more than 1 ms). All speed parameters of hard drives can be measured using the appropriate utilities, but you should not rely entirely on your own feelings or on the readings of the system monitor, because the read/write speed in applications is highly dependent on many other factors.

The speed of the hard drive (transfer and seek) significantly depends on its rotation speed, which is measured in revolutions per minute (rpm). Sometimes sellers quote very high transfer speeds (say, 66 or 100 MB/s). This relates to the interface bandwidth and the real speed of the disk has approximately the same relation as, say, the size of the head has to the mental abilities of a person. To a much greater extent, the speed of the disk is determined by the speed of rotation of the planes. Here typical values are 3600, 4500, 5400, 7200, 10000, 15000 revolutions per minute (rpm). The most preferable are discs with a rotation speed of at least 7200 rpm.

3. Recently, another parameter has become important - recording density. Hard drives with so-called “double density” have appeared. They are distinguished by high transfer, since at the same disk rotation speed more is read from it per revolution. As a rule, the density of such disks is over 1 GB per package disk inside the hard drive (that is, a 1.7 GB disk has only one disk inside, a 3.6 GB disk has two, etc.).

The technology developed by IBM for manufacturing media with a special coating will make it possible in the near future to produce inexpensive magnetic drives with a capacity of up to 1 TB. And the transition from traditional longitudinal magnetic recording to perpendicular one will allow increasing the recording density to 1 TB/inch 2 and obtaining three-inch disks with a capacity of several terabytes.

2. Optical and magneto-optical storage devices. Currently, an integral part of the computer configuration is a disk drive (drive) for reading CD-type media (CD and DVD).

Compact discs (CDs) There can be write-once CD-R and write-once (rewritable) CD-RW.

In CD-R discs, the reflective layer is made of gold film. Between this layer and the polycarbonate base there is a recording layer of organic material that darkens when heated. During the recording process, the laser beam heats selected points of the layer, which darken and stop transmitting light to the reflective layer, forming areas similar to depressions, i.e. bit cells (pits). Information is composed by alternating pits and spaces between them (that is, binary zeros and ones) (Figure 3.20).

Figure 3.21 – CD track

Unlike magnetic disks, CDs do not have many ring tracks, but one – spiral, like gramophone records, going from the center to the periphery. In this regard, the angular speed of rotation of the disk is not constant. It decreases linearly as the laser reading head moves towards the edge of the disk. For every inch (2.54 cm) of the radius of the disk there are 16 thousand turns of a spiral track. For comparison, only a few hundred tracks fit per inch radius on the surface of a hard drive. The capacity of one CD reaches 640-800 MB. In order for the media to function, a fairly large amount of service information (about 8 MB) is also written to it, so the usable capacity of the CD is somewhat lower than indicated.

CD-R drives, thanks to their significant reduction in price, are becoming increasingly widespread. Information on CDs, unlike magnetic media, is practically not susceptible to the destructive effects of electric and magnetic fields. However, it requires careful handling on the part of the user. Any mechanical damage and exposure to a number of chemical solutions will damage the disk. Today, practically only CDs are used for legal delivery of software products, etc.

The multiple write system was originally called CD-E ( CD-Eraseable), but then the name was changed to CD-RW ( CD-ReWritable). CD-RW uses an intermediate layer of organic film, which changes its phase state from amorphous to crystalline and back under the influence of a laser beam, resulting in a change in the transparency of the layer. The recording of changes in state occurs due to the fact that the material of the recording layer, when heated above a critical temperature, goes into an amorphous state and remains in it after cooling, and when heated to a temperature significantly below the critical temperature, it restores the crystalline state. Existing drives can withstand thousands to tens of thousands of rewrite cycles. However, their reflectivity is significantly lower than stamped and write-once CDs (you will notice that the surface of a CD-RW is much darker than the surface of a regular CD or CD-R).

A rewritable disc can either have the same track structure and file system as a CD-R, or (more often) it has a special UDF file system ( Universal Disk Format), allowing you to dynamically create and destroy individual files on disk. For example, you can use a CD-RW as a regular removable disk and write to it directly from applications.

Probably, everyone who has ever dealt with one or another CD/DVD reading drives has paid attention to one design feature of the structure of these devices - a round recess with a diameter of 80 mm inside a large circle of 120 mm in size for regular CDs. This is the place for 80mm CDs. The fact that this recess has not yet disappeared from the tray of CD and DVD devices can be explained by the fact that discs with a diameter of 80 mm are still an ISO standard. The capacity of such disks is 180 MB. This type of CD also has its younger brothers. This is a family of so-called business card CDs. In fact, these are ordinary disks, but cut on both sides, so that they resemble a business card in appearance and size. Depending on the degree of cutting, the capacity of such CDs can vary from 20 to 60 MB. It should be noted that 80 mm discs gradually developed and reached the CD-R/RW stage. Today, such CD-R/RWs are sometimes used in digital photo and video cameras.

The disc is read using a regular drive. A drive that can not only read, but also write to CDs is called a recorder. All modern CD recorders can handle both CD-R and CD-RW, although in the past you needed a special device to use CD-RW. As a rule, rotation speed is indicated in three numbers. The first usually characterizes CD-R recording, the second CD-RW recording, and the third means reading speed. For example, 6x/4x/24x means CD-R write speed is 6x, CD-RW is 4x, and disc read speed is 24x.

Drive characteristics: drive speed. The rotation speed of a CD-ROM (200-4200 rpm) is related to the speed at which audio and video data are transferred from the drive to the main memory of the computer. In this regard, the concept of drive speed was introduced. The speed of the drives is measured relative to the rotation speed of a conventional music CD player (transfer speed is about 150 kB/s). It is measured in multiples. For example, the 40x setting means the drive can spin the disc 40 times faster than a standard CD player. A single speed drive is designated 1x; Its data transfer speed is 150 kB/s. Currently, drives with a speed of 32x are used (4800 kB/s; on external tracks the transfer speed reaches the nominal (for example, 1800 kB/s), and as it approaches the internal ones it drops (in our example to approximately 1200-1300 kB/s) As a result, even with significantly different disk rotation speeds, modern drives of fairly high quality have generally the same data transfer speed; access time (time spent searching for the necessary data) is 400 ms; for the best models it is about 80-60 ms. however, cheap ones can have much more - up to several hundred ms. Moreover, cheap drives also have such remarkable features as poor disk reading quality (for example, disks with defects, which are perfectly readable on other drives, may not be readable at all or may not be readable on them). lower speed), strong noise, vibration (sometimes it even becomes scary when the computer literally starts bouncing on the table) and other not very pleasant qualities of low-grade products. However, they have a very short service life; it is quite possible that the drive will break down after just a few months of use.

DVDs(Digital Video Disk - digital video disk or Digital Versatile Disk - digital multifunctional disk). Unlike CD, it has a higher data density, the possibility of double-layer recording and more advanced protection of licensed discs from pirated copies.

What are the main differences between the DVD standard and the CD standard? First, a laser with a shorter wavelength is used. If the wavelength in CD–R drives is 780 nanometers, then in DVD drives it is 635 nanometers. This allows you to reduce the stroke length and increase the speed of data reading. Secondly, due to the use of more advanced materials, DVDs are used to record data in two layers on one side of the disc, or one layer on both sides of the disc, or two layers on both sides of the disc, depending on the DVD format. Disk capacities vary from 2.6 GB to 17 GB. Third, a completely new sector format, more reliable error correction code and improved channel modulation are used.

The following DVD structure types exist:

Single Side/Single Layer This is the simplest structure of a DVD disc. This disk can store up to 4.7 GB of data. By the way, this capacity is 7 times greater than the capacity of a regular audio CD and CD-ROM disc;

Single Side/Dual Layer The disks have two layers of data, one of which is translucent (to allow the laser beam to access the inner layer). Both layers are read from one side and such a disk can accommodate 8.5 GB of data, that is, 3.5 GB more than on a single-layer/single-sided disk;

Double Side/Single Layer This disk holds 9.4 GB of data (4.7 GB on each side). It is easy to see that the capacity of such a disc is twice that of a single-sided/single-layer DVD. Meanwhile, due to the fact that the data is located on both sides, you will have to flip the disk over or use a device that can read the information on both sides of the disk on its own;

Double Side/Double Layer (double-sided/two-layer). The most difficult option. Provides the ability to store up to 17 GB of data on the disk (8.5 GB on each side). It is clear that such a disc is essentially two single-sided/double-layer discs folded together.

Note that all figures given correspond to capacity specified in billions of bytes, and not in regular computer gigabytes. In reality, it will be 4.38 GB, 7.95 GB, 8.75 GB and 15.9 GB, respectively.

All information on DVD is stored in the MicroUDF (Micro Universal Disk Format) file system. It was officially approved in 2000. MicroUDB supports high-capacity media and large file sizes. File names are written in UNICODE format, which ensures DVD compatibility with all PC operating systems, as well as with a variety of household appliances.

As for the drives themselves, they have a higher disk rotation speed than CD-ROMs, and the one-time rotation speed of a DVD corresponds to approximately three times the rotation speed of a CD. However, due to the denser data packing of DVDs, data transfer speeds at 1x are roughly equivalent to 9 times the speed of a CD-ROM, which is about 1.3 MB/s. Therefore, for DVD-ROM drives, two speeds are indicated: DVD rotation speed and CD rotation speed (which in revolutions per second is, in principle, approximately the same thing). What's true for CD-ROMs also applies to DVD-ROM devices - bigger doesn't always mean better, and it's better to pay attention to the workmanship of the device rather than the numbers in its name. Due to the higher recording density, DVD access time is several tens of milliseconds higher than that of CD, but the same parameter when handling a CD is approximately the same (or differs slightly) as on CD-ROM drives.

Magneto-optical technology made it possible to create disk drives with huge information capacity (units of Terabytes). An MO disk can be rewritten multiple times, has an increased durability of data storage (up to 100 years) and provides higher operating speed (several times). However, this technology still has an increased cost.

An MO disk is a polycarbonate substrate (often also called a layer) 1.2 mm thick, onto which several thin-film layers are applied, which contains the magnetic part of the technology, and the optical part is represented by a reading laser (Figure 3.22).

Figure 3.22 - Magneto-optical disk

IN Blu-ray discs“blue”, or rather blue-violet laser technology is used (in contrast to DVD, which is based on classic red laser technology) with a wavelength of 405 nm. This reduction made it possible to narrow the path by 2 times.

A single-layer disc can store 25 GB. A dual layer disc can support 50 gigabytes. Blu-ray is easily enhanced to include support for multilayer discs, which can
wives allow you to increase the storage capacity to 100−200 GB.

Due to the fact that the data on Blu-Ray discs is located too close to the surface, the first versions of the discs were extremely sensitive to scratches and other external mechanical influences, which is why they were enclosed in plastic cartridges. This shortcoming raised serious doubts about whether the Blu-ray format could hold its own against its main competitor, DVD.

The solution to this problem appeared in January 2004 with the advent of a polymer coating, which gave drives incredible protection against scratches and dust. This coating, developed by TDK Corporation, is called "Durabus", it allows them to be cleaned with wipes, which can damage CDs and DVDs.

Blu-ray uses an experimental security element called BD+, which allows the encryption scheme to be dynamically changed. Once the encryption is broken, manufacturers can update the encryption scheme and all subsequent copies will be protected by the new scheme. Thus, a single cracking of the cipher will not allow the entire specification to be compromised for the entire period of its life.

3. Magnetic tape drive. Such a carrier is a streamer. tape streamer) - a device for backing up large amounts of information in compressed form (file types arj, .jpeg, .zip, etc.). Storage devices can be built-in or external. Most drives have a SCSI interface. The streamer's information carrier is magnetic tape (usually with a layer of iron oxide) with a typical width of 4-5 mm (Tape Drives). The tape is wound on two reels and placed inside a cassette (cartridge). Outwardly, it resembles a household tape recorder cassette (Figure 3.23).

There are currently various QIC standards ( Quarter Inch Cartridge quarter-inch cartridges), DAT ( Digital Audio Tape - digital audio recording), DDS ( Digital Data Storage - digital data storage), DLT ( Digital Linear Tape - digital linear recording) and LTO ( Linear Tape Open - open linear tape standard), defining the parameters of tape drives and cassettes for them. The capacity of magnetic tape media is from 150 MB and above. Number of tracks 20-144. Recording density 10,000-100,000 bpi. Data transfer speed 2-60 MB/min. Tape length 62.5-360 m.

Figure 3.23 - Cassette for streamer

QIC cassette drives have relatively low performance. This is partly due to their connection to the floppy drive interface.

For now, the largest volumes of information can be stored on DLT7000 standard drives (up to 35 GB with a SCSI-II Fast/Wide interface and data transfer speeds of up to 10 MB/s).

4. Solid State Memory, or solid state drive (Solid State Disk, SSD) is represented by semiconductor non-volatile flash memory. It does not contain moving parts, as it is often built on single-transistor memory elements. Currently popular flash memory standards are CompactFlash, SmartMedia and Secure Digital. The memory capacity in one design does not yet exceed several gigabytes (Figure 3.24).

Figure 3.24 - Flash drive

Initially, the memory was presented in the PC Card design (PCMCIA standard) with a capacity of 2 to 64 MB. Such memory is intended for use in portable devices, for example, digital cameras, cell phones, players, pocket computers - organizers and handheld gaming devices. Connecting a flash drive to a computer is most often done via a USB port.

To operate Flash disks of the Linear Flash type (according to the standard of the International Association of Memory Cards for Personal Computers), special software is required: drivers - Flash File System or conversion level programs - File Translation Layer. At the same time, memory cards such as PC Card ATA Flash (ATA flash card) do not need such support, since they are supported by the operating system.

Standard programs and utilities are used to determine the speed and performance of USB flash drives.