Comparison of different types of storage media. Data storage device

Storage and information carriers.

Information storage device -   a device that reads and / or writes information.

Information storage can be:

· internal and external:

· with removable and non-removable media;

· stationary and portable.

Internal storage is in the system unit   PC and connect to special connectors on the motherboard.

External and portable drives are in their own enclosure and are connected to the computer via standard I / O ports. External storage devices are used for reserve copy   and storage of information, as well as for transporting data from one computer to another.

Information carrier   Is a device on which information (eg, a disk, a tape cartridge, etc.) is directly stored (stored).

The storage device and the storage medium can be made in one housing, i.e. make up one whole, for example, a hard diskHDD (Figure 13).

Fig. 13. Hard drive on a hard disk HDD

The drive can have removable media, for example:

· The FDD drive   removable media - floppy disk (Floppy-disc);

· For a DVD-RW drive   (Figure 14) removable media -DVD-disc.

Fig. 14. DVD-RW Drive

In some cases, the division into a drive and a carrier is conditionally. For example, internal storage of information RAM (RAM ) and portable storageFLASH -cards are both a storage medium and a carrier of information.

Main drives and storage media

The main characteristic of the medium (storage) is its capacity, i.e. the maximum amount of information that can be written to this device. The capacity of the drive is measured in the following units:

Latelyfloppy discs and CD -Discs are obsolete, will soon cease to be used and actively replaced by more capacious carriersFLASH cards (Figure 15) andDVD-discs.

Fig. 15 .. FLASH-card

Capacity of the main media (drives).

go out of use

CD

650 Mb, 700 Mb

go out of use

DVD

4.7 Gb, 9 Gb

DVD-disks can be single-sided and double-sided, single-layered and double-layered

FLASH card

256 Mb, 512 Mb,

1 Gb, 2 Gb

Internal media / storage media

RAM memory

512 Mb

1 Gb

standard for Windows XP

standard for Windows Vista

HDD HDD

120 - 300 Gb

Typical capacity of a modern PC

External data storage devices came somehow unexpectedly into our lives. It can be said, abruptly. Currently, people highly appreciate the mobility of information, as well as the speed of its transfer. That's why an external storage device is a very valuable device that allows you to quickly exchange movies, games and other files (it should be noted, even a considerable size) between two computer devices.

general information

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

The optimal currently are, of course, various networked storage facilities, which in many companies are located right inside the buildings. In general, they have many advantages. Previously, the creation of a network storage required the purchase of a separate computer that would play this role. Now, with the development of wireless technologies, this is no longer necessary. It is enough to enter the wireless router into the business - and the problem is solved.

Modern models are available with support for USB 3.0 ports. And this also has weight, because the functionality is greatly expanded. What better way to think up than a network resource that is at home, which, if necessary, is quite realistic to take with them on a trip? And this device will be so mobile that it does not burden absolutely nobody with its carrying!

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

So, many hard drives now have an interesting innovative interface. It's about USB 3.0 ports. They also have a great form factor. Next, we'll talk about whether there is any sense in acquiring such disks, which are of sufficiently large size, require power from an external source.

ADATA HD 710

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

This external storage drive is released in three colors at once. The following colors are available: blue, yellow, black. All hard disks, belonging to this series, have a shockproof and waterproof casing. You can lay the USB cable without any problems in the groove, which was specially fixed around the disk housing. Thus, the developers of the device solved the problem with the convenience of storing the cable. Its length is about 30 centimeters. And to be more precise, 31. The dimensions are quite averaged: with its mass 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 at once, each equipped with a different amount of built-in long-term memory. We are talking about variations in the volume of 500 gigabytes, as well as models with a capacity of 1 TB and 1.5 TB.

Among the shortcomings is worth noting the lack of legs, which could deal with the vibration of the hard drive during its operation. But the use of matte plastic as a material for the hull can not be clearly considered. The USB cable does not fit anywhere. It has a length of 43 centimeters. This external hDD   length is 126 millimeters, width - 80, and in height - 15.

Seagate Expansion Portable

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

Like the model we saw earlier, Seagate Expansion Portable does not have legs made of rubber. The case of the devices of the series is made of matte plastic. These external storage   have a USB cable 44 centimeters long. The 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

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

Cable type USB 3.0 has a length of 118 centimeters. For hard work   you need a special power adapter. It operates at a voltage of 12 volts, as well as with a current of 1.5 amperes. The length of such a drive reaches 179.5 millimeters. In width - 118 millimeters, and its height is 37.5 mm. The mass of the drive is 940 grams.

Silicon Power Armor A80

External storage of this series have a good body, protected from moisture penetration, as well as from mechanical damage. The outer surface of the hard disk is made of anodized brushed aluminum. To resist the vibration that occurs when working with the drive, rubber feet are not provided.

The model line consists of disks with three different volumes of memory. This is 1 and 2 terabytes, as well as 500 gigabytes. The models of the series are slightly different from all external storage devices, which we considered earlier. The fact that they have just two cables, which are designed to synchronize the device with a personal computer or laptop. The first cable has a length of 79 centimeters. The second is shorter by 70 cm. The body 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 the models that have been described previously use USB 3.0 Micro-B. With a mass of 270 grams, the hard drives of the series have a size of 139.45 mm by 94 mm by 18.1 mm.

TOSHIBA Stor.E Basics

The case of this line of external memory drives is made of matte plastic black. At the bottom of the gadget are four legs, which simply can not but rejoice. But as for the volume, then the series can not please all users. The maximum amount of long-term memory that is available in such drives is 1 terabyte. The remaining two versions of the series have, respectively, the volume of 500 GB and 750 GB.

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

Transcend StoreJet 25H3

External discs of this brand have a body that is covered with a rubber layer. Thus, the manufacturer was concerned about mechanical strength, adapting the external hard drives of this series to unexpected mechanical shocks and loads. Models produced in the lineup have a memory capacity of 500 gigabytes, as well as 1 and 2 TB. If we talk about the color solution, then the hard drives of the series are available in violet-black design, as well as in blue. The length of the cable for synchronization with the PC is about 45 centimeters.

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

Western Digital My Passport Ultra

Like almost all other models, the series of this external hard-drive memory is made of matte plastic of black color. At the bottom there are four legs that will save the device from vibration during operation. The hard drive cover, depending on its modification, can be different color. At the moment, black, blue, red and metallic colors are available.

The amount of built-in memory is standard: 500 gigabytes, 1 TB or 2 TB. The USB cable does not stack 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. The overall dimensions are also different. The length can be from 110 to 110.5 millimeters, width - from 81.6 to 82 millimeters. It's not so noticeable, but how the thickness of the hard drive grows with the increase in its memory capacity is seen quite well. It falls in the interval from 12.8 to 20.9 millimeters.

A data storage device is a device on which all computer data is stored. In addition to the drive, this device is called hard drive   or a hard drive. A hard disk from a conventional "flexible" disk, or in other words, a floppy disk, differs in that the recording of information occurs on hard plates made of aluminum or ceramics, and on top they are covered with ferrimagnetic material. Hard drives are equipped with one or more plates on the axis.

The data storage device (HDD) includes a sealed unit and an electronic board. The sealed unit is filled with ordinary, dust-free air, by atmospheric pressure, and its equipment includes all mechanical parts. The kinematics of the data storage device includes one or more magnetic disks, which are rigidly fixed to the spindle of the motor, and also a system responsible for positioning the magnetic heads. The magnetic head occupies a place on one side of the moving magnetic disk and its functional duties include reading and writing data from the rotating surface of the magnetic disk. The heads themselves are attached by special holders, and their movement is carried out by means of a positioning system between the edge and the center of the disk. Achieve accurate positioning of the magnetic heads is possible by servo information recorded on the disk. The positioning system, reading this information, is able to determine the current that passes through the coil of the electromagnetic wire so that the magnetic head can lock over the necessary track.

After the power is turned on, the HDD (drive) processor begins to test the electronics, after which the command is issued so that the process of direct switching on the spindle motor is carried out. As soon as the initialization is completed, the positional system is tested, during which the track is traversed, in the specified sequence. In case the testing went well, the hard drive sends a signal that it is ready to work. To improve the reliability of storage of computer information, hard disks (drives) are equipped with a special microprogram that monitors the technological parameters available for the reading and analysis program. If the computer is threatened with a crash, then with the help of this program the user will know about it in a timely manner.

In addition, the data drive is also a hybrid hard disk, which consists of a traditional hard disk equipped with additional flash memory. This flash memory is completely non-volatile and has a buffer role in which data most often used is stored. As a result of the activity of this device, access to the magnetic disk is reduced, which consequently leads to a decrease in electricity consumption. Also, the level of reliability of information storage is increased, the time required for downloading and for outputting the system from the sleep mode state is reduced, and the temperature and acoustic noise produced by the hard disk is significantly reduced.

The device of all hard disks is completely analogous and all types of data storage devices can go out completely, so the main thing is to remember to each user that in order for the hard disk to be as reliable as possible it must be properly operated. Namely, protect from overheating, shock, increased body vibration, frequent on or off. In addition, you do not need to use a power supply that is of poor quality.

In most laptops, you can not insert a second hard drive, and the main change is not always easy. External memory stores come to the rescue.

For storing, transferring and backing up data in computer systems, external storage devices are used. The main types of such drives are devices based on hard drives and flash memory. In some cases, such drives are used external drives   optical discs, but since most computers have internal disk drives for reading and writing CDs, DVDs or Blu-ray discs, these drives have limited distribution and we will not dwell on them here (more on optical drives   read in a separate article).

Flash Drives

Due to lower prices for flash memory, external storage devices on its basis are becoming more widespread. A typical flash drive is a small, one-time lighter size device with a built-in USB connector. In this case, the volume of such miniature drives can vary in a very large range: from one to 128 GB. To date, the most popular models with a capacity of 8 to 16 GB can be purchased for 500-900 rubles, a little more expensive are estimated modifications in protected rubberized and hermetic aluminum cases. As a rule, flash drives for 8-16 gigabytes are purchased not for storage and backup, but for efficient data transfer.

Significantly more expensive high-capacity flash drives: 64 GB models are estimated at about 5000 rubles, and 128 GB - at 11,000 rubles and more. It is not difficult to calculate that the cost of gigabytes disk space   in such drives about a half times higher (from 85 rubles) than in the storage of small capacity. In addition, an external mini-hard drive of the same volume will cost about three times cheaper. Therefore, consumers prefer it to them.

External HDs

The optimal solution for storing and backing up large volumes of data has been for several decades now hard drives. Modern hard drives are distinguished by high reliability, high capacity and low cost of data storage: in the best models, it ranges from 3 to 4 rubles per gigabyte.

External hard drives can be divided into four big categories: 2.5-inch drives, 3.5-inch drives, multimedia drives and NAS systems.

Drives based on 2.5-inch "notebook" hard drives are the most miniature: they are considered portable and easily fit into a shirt pocket. However, in comparison with 3.5-inch disks they are much lower than the speed of writing and reading, the capacity is limited, and the cost of gigabytes of storage is 1.5-2 times higher. Typical for such drives read speed - 35 MB / s, records - 30 MB / s, the best models speed reading and writing can reach 50 MB / s.

The volume of 2.5-inch external hard drives - from 120 to 500 GB, the cost of storing a gigabyte of data is, on average, from 8 to 12 rubles.

Typically, 2.5-inch hard drives are equipped with a USB 2.0 interface, sometimes eSATA and almost never support FireWire, except for ZIV-branded disks. In many cases, for such drives, there is enough power supplied through the USB bus.

It is also worth mentioning models based on 1.8-inch "subnotebook" hard drives, which are even smaller than 2.5-inch. Typically, the capacity of such drives is limited to 120 GB and they are equipped exclusively with a USB 2.0 interface. In stores these discs are rare, usually they are distributed at various events as souvenirs.

The most popular and popular category is external drives based on standard 3.5-inch hard drives. They can consist of one or two hard disks located in one casing, and in the latter case it is usually possible to organize RAID arrays of levels 0 (merging disks) and 1 (mirroring).

For drives based on 3.5-inch hard drives, read speed is 70-90 MB / s and the write speed is 60-80 MB / s. In the most productive models, the reading speed can reach 120 MB / s, and the recording speed is 110 MB / s. The volume of such drives is usually from 500 GB to 2 TB in single-drive models and up to 4 TB in dual-drive ones. The cost of storing one gigabyte, on average, is from 4 to 8 rubles, for the best models - from 3 to 4 rubles.

3.5 inch external drives   can be equipped with a full range of various modern interfaces: in addition to mandatory USB 2.0, they install eSATA, FireWire 400 and FireWire 800 controllers, as well as a promising USB 3.0 interface.

Multimedia drives are a special category of external hard drives based on 2.5- or 3.5-inch hard drives, which are equipped with a built-in decoder of popular audio and video formats, as well as a software media player with hardware controls. In fact, these drives are multimedia players based on a hard drive and are usually equipped with a remote control.

Such devices can be directly connected to the TV and audio system and they will act as a standalone multimedia player, not connected with the computer. To do this, they are equipped with "home" video interfaces (composite, component, HDMI), as well as analog and digital audio outputs. In many cases, these devices are embedded in a card reader, which allows you to directly play multimedia content from removable flash cards. There are modifications designed exclusively for connecting removable hard drives, purchased separately.

In the standard arsenal of multimedia drives - support for video formats MPEG-1/2/4, DivX and XviD, audio formats MP3, WAV, AAC, as well as digital jPEG images. The possibility of working with other formats should be specified separately when selecting each particular model.

Of course, such devices can also be used as ordinary computer external storage devices - usually via USB 2.0 and eSATA interfaces.

The most complex and expensive type of external storage devices are NAS systems, that is, networked data stores. These are external devices with one or several 3.5-inch hard drives, equipped with a network interface Ethernet (all modern models - Gigabit) and have the functionality of a mini-server.

NAS drives are network computers, the main function of which is to provide access to the data stored in them for any computer that is part of the local network. Moreover, many of these devices have the expanded functionality of a "real" server, able to connect to the Internet and exchange data via FTP and HTTP protocols.

In some NAS built-in multimedia servers that allow you to play and broadcast stored on the hard drive content on the local network, as well as print servers: connected to the NAS printers will be available to all computers that are part of the network. Many models are equipped software   for data backup.

However, the most popular function for which NASs are most often purchased or assembled is the built-in peer-to-peer client, which allows you to download and download files from BitTorrent and eMule networks, not including a computer. Such devices are capable of working around the clock, consuming much less electricity than a full-fledged PC, and practically without making noise (however, this depends on the specific design).

Despite the fact that NAS drives are usually built on the basis of 3.5-inch disks, they are often inferior to 2.5-inch external hard drives in terms of performance. Manufacturers rely on reliability, rightly believing that low speed   access through local area network   It makes no sense to use discs with high speed characteristics. Of course, when you directly connect to a computer via USB 2.0 or eSATA interfaces, the drives demonstrate quite normal for 3.5-inch hard drives.

The prices for NAS-drives vary in a fairly wide range: extremely simple single-disk models without an FTP / HTTP server cost about 4000 rubles, and multifunctional systems with support for five hot-swappable hard disks can cost more than 30,000 rubles. At the same time, for quite a small amount of money, you can build NAS yourself from an old computer or from inexpensive components for nettops. For such a "self-gathering" often use a special and completely free assembly operating system   FreeBSD, called FreeNAS. This software allows you to configure the network storage of data with almost any necessary functionality.

Introduction

1. Magnetic Drives

1.1. Drives on magnetic disks

2. Types of magnetic carriers

2.1 Flexible magnetic disks

3. Optical technologies

3.1 CDs

3.2 DVD Media

Conclusion

Bibliography

magnetic hard drive   magnetic

Introduction

The released data storage devices are a gamut of storage devices with different operating principles with physical and technical performance characteristics. The main property and purpose of data storage devices is its storage and playback.

Storage devices are divided into types and categories in connection with their operation principles, operational-technical, physical, software and other characteristics. For example, according to the principles of operation, the following types of devices are distinguished: electronic, magnetic, optical and mixed - magneto-optical.

Each type of device is organized on the basis of an appropriate storage technology for playback / recording digital information. Therefore, in connection with the type and technical performance of the information carrier, there are distinguished: electronic, disk and tape devices.

Magnetic disks are used as memory devices that allow storing information for a long time, with the power turned off. To work with magnetic disks, a device called a magnetic disk drive (HDD) is used. The main types of drives: drives on floppy disks (floppy disks); Hard disk drives (HDD); tape drives (NML); CD-ROM, CD-RW, DVD.

They correspond to the main types of media: flexible magnetic disks (Floppy Disk); hard disk drives (Hard Disk); cassettes for streamers and other NML; CD-ROM, CD-R, CD-RW, DVD.

1. Magnetic storage

Magnetic drives are the most important medium for storing information in a computer and are divided into tape drives (NML) and magnetic disk storage (HDD).

Usually, magnetic recording uses impulse signals. Bit information is converted to alternating current in accordance with the alternation of zeros and ones.

This current flows to the magnetic head and, depending on the direction of the current in the head winding, a corresponding magnetic flux is formed in the space between the head and the carrier, which closes through the elementary region of magnetization (domain). The intrinsic magnetic fields of the domains are oriented in accordance with the direction of the external magnetic field. When the external field is removed, this state of domains does not change (long-term storage memory).

The main criterion for estimating storage devices on magnetic media is the surface recording density. It is defined as the product of the linear recording density along the track, expressed in bits per inch, and the number of tracks per inch. As a result, the surface recording density is expressed in megabits (Mbit / in2) or gigabit (Gb / in2) per square inch.

In modern 3.5-inch drives, the value of this parameter is 10-20 Gb / in, and in experimental models it reaches 40 Gb / in. This allows you to produce storage capacity of more than 400 GB.

1.1. Drives on magnetic disks (NMD)

In NMD, a similar NML is provided for the possibility of sequential access to information. A magnetic disk storage device combines several serial access devices, and the reduction in the data retrieval time is ensured by the independence of access to the record from its location relative to other records.

Technology NMD. In NMD as a data carrier, a package of metal disks (or payers) fixed to a rod around which they rotate at a constant speed is used. The surface of a magnetic disk covered with a ferromagnetic layer is called a working one.

The number of magnetic heads is equal to the number of working surfaces on one package of disks. If the package consists of 11 disks, the access mechanism consists of 10 holders with two magnetic heads on each of them. Holders of magnetic heads are united in a single unit in such a way as to ensure their synchronous movement along all the cylinders. The totality of the tracks achieved with a fixed position of the head block is called a cylinder. The distance between the cylinders (tracks) is called the feed, or the pitch of the track. The process of controlling the recording density is called precompensation. To compensate for different recording densities, the ZoneBitRecording method is used, where the entire disk space is divided into zones (eight or more), each of which usually contains 20 to 30 cylinders with the same number of sectors.

In the zone located on the outer radius (the lowest zone), a greater number of sectors (blocks) are recorded per track (120-96). To the center of the disk, the number of sectors decreases and in the oldest region reaches 64-56. Since the disk rotation speed is a constant value, more information comes from external zones with one disk revolution than from internal zones. This unevenness of information is offset by an increase in the speed of the data reading / conversion channel and the use of special tunable filters for frequency correction by zones. At the same time, the capacity of hard drives can be increased by approximately 30%.

1.2 Hard disk drives

Design and operation of the device. In the HDD, several plates (disks) or platters are installed inside the drive. The plates have a diameter of 5.25 or 3.5 inches. In new developments, glass is being tried, because it has more resistance and will make discs thinner than aluminum counterparts.

Characteristics of HDD. The characteristics of the hard disk are very important for assessing the performance of the system as a whole. The effective speed of the hard drive depends on a number of factors.

The decisive among them is the disk rotation speed, which is measured in rpm (rpm) and directly affects the data transfer rate in the HDD. While the fastest HDDs with an EIDE interface had a speed of about 5400 rpm, the SCSI-HDD is capable of accelerating to 7200 rpm. The average disk access time is the interval between the time the data is requested and the time it is accessed (measured in milliseconds (ms)). The access time includes the actual search time, the waiting time, and the processing time.

Search time - the total time required to search the read / write head for the physical location of data on the disk. The latency is the average time to access the sector during the rotation process. It is easily calculated from the rotational speed of the drive axis as a half-turn time.

The transfer speed of the disk (sometimes called media-speed) is the speed at which data is transferred to the drive and read from it. It depends on the recording frequency and is usually measured in megabytes per second (MBps, MB / s).

The data transfer rate (or DTR-DataTransferRate) is the speed at which the computer can transmit data via buses (usually IDE / EIDE or SCSI) to the CPU. Some data providers indicate the internal transfer rate, data transfer from the head to the built-in disk buffer. Others lead the data packet transfer rate, the maximum transmission rate for ideal parameters or for a short duration. The speed of external data transmission is more important.

2. Types of magnetic carriers

2.1 Flexible magnetic disks

The diskette consists of a round polymer substrate, covered on both sides with magnetic oxide and placed in a plastic package, on the inner surface of which is applied a cleaning coating. In the packaging on both sides, radial slots are made through which the read / write heads of the drive get access to the disk.

Diskettes of each type are usually two-sided. The single track density is 48 tpi (lanes per inch), double is 96 tpi and high is usually 135 tpi.

When a 3.5 "disc is inserted into the device, the protective metal shutter moves away, the drive spindle enters the middle hole, and the side pin of the drive is placed in a rectangular positioning hole located side by side. The motor rotates the disc at a speed of 300 rpm.

Floppy disk drives use the so-called "open loop tracking", they do not actually look for a track, they just set the head to the "correct" position. AT hard disks, on the contrary, the servomotor motors use heads to check positioning, which makes it possible to record with a transverse density many hundreds of times higher than is possible on a floppy disk.

The head is moved by the lead screw, which in turn is controlled by the stepping motor, and when the screw is turned to a certain angle, the head passes the set distance. The density of writing data to a floppy disk is limited by the accuracy of the stepper motor, in particular, this means 135 tpi for diskettes 1.44 MB. The disk has four sensors: a disk motor; write protection; the presence of a disk; and track sensor 00.

2.2 External hard drives on the HDD

In recent years, technologies for placing standard HDDs in a mobile (portable) external case (box) that has been connected to the computer via an external interface have spread.

Since today the capacity of HDD is measured in gigabytes, and the dimensions of multimedia and graphic files   - tens of megabytes, capacity from 100 to 150 MB is enough to make the media occupy the traditional niche of floppy disk - moving several files between users, archiving or backing up individual files or directories and sending files by mail. In this range, a number of devices are proposed for the next generation of floppy disks that use flexible magnetic media and traditional magnetic storage technology.

Zi p-stores   . Without a doubt, the most popular device in this category is the ZipIomega drive, first released in 1995. The high efficiency of Zip drives is provided, firstly, by a high rotation speed (3000 rpm), and secondly by the technology offered by Iomega (which based on the aerodynamic effect of Bernoulli), while the floppy disk "sucked" to the read / write head, and not vice versa, as in the HDD. Disks Zip soft, like flexible disks, which makes them cheap and less susceptible to shock loads.

Zip-drives have a capacity of 94 MB and are available in both built-in and external versions. The internal modules correspond to the 3.5-inch form factor, use the SCSI or ATAPI interface, the average search time is 29 ms, and the transfer rate is 1.4 KB / s.

Superdiscites.   The range from 200 to 300 MB is best matched by the concept of a territory of superdiscade. The capacity of such devices is 2 times higher than that of an alternate floppy disk drive, and is more characteristic for HDD than for a floppy disk. Devices in this group use magnetic or magneto-optical technology.

In 2001, Matsushita announced the FD32MB technology, which gives an option for high-density formatting of a conventional HF floppy disk at 1.44 MB to provide storage capacity of up to 32 MB on disk. The technology consists in increasing the recording density of each track on a HD floppy disk using a superdisk magnetic reading head and a conventional magnetic head for data recording. While 80 circular data tracks are placed on a conventional floppy disk, in FD32MB this number is increased to 777. At the same time, the feed of a track from 187.5 μm for a floppy disk HD is reduced to about 18.8 μm.

Replaceable Hard Drives   . The next capacity interval (from 500 MB to 1 GB) is sufficient to backup or archive a disk partition (partition) of a reasonably large size.

In the range of more than 1 GB, removable disk technology is borrowed from conventional HDDs. Released in mid-1996 drive IomegaJaz (replacement hard drive for 1 GB) was perceived as an innovative product. When Jaz appeared on the market, it immediately became clear where to use it - users could create audio and video presentations and transfer between computers. In addition, such presentations could be launched directly from the Jaz media, without having to rewrite the data on the HDD.

Flash Memory   . Not referring to magnetic media, flash memory works simultaneously random access memory   and HDD. It reminds ordinary memory in the form of discrete chips, modules, or memory cards, where, just as in DRAM and SRAM, data bits are stored in memory cells. However, just like the HDD, the flash memory is nonvolatile and saves data even when the power is off.

Technology ETOX is the dominant flash-technology, which occupies about 70% of the entire market of nonvolatile memory. The data is entered into flash memory bit by bit, by byte or by words using an operation called programming.

Although electronic flash drives are small, fast-acting, consume little power and can withstand impacts of up to 2000g without the destruction of data, their limited capacity makes them an inappropriate alternative to the PC hard drive.

3. Optical technologies

3.1 CDs

Initially, CDs were used exclusively in high-quality sound reproducing equipment, replacing obsolete vinyl records and tape cassettes. However, soon laser discs were also used on personal computers. Computer laser discs were called CD-ROM. In the late 90's. device for working with CD-ROM became a standard component of any personal computer, and the vast majority of programs began to be distributed on CD-ROM.

The drive is on a CD-ROM (CD-ROM). The reading of information from the CD-ROM occurs with the help of a laser beam of lower power. The servomotor, upon command from the internal microprocessor of the drive, moves the reflecting mirror or prism. This allows you to focus the laser beam on a specific track. The laser emits coherent light, consisting of synchronized waves of equal length. The beam, reaching the light reflecting surface (pad), through the splitting prism, is deflected to the photodetector, which interprets this as "1", and falling into the depression (pit) is dissipated and absorbed - the photodetector fixes "0".

While the magnetic disks rotate at a constant number of revolutions per minute, i.e. with a constant angular velocity, the CD rotates usually at a variable angular velocity to ensure a constant linear speed during reading. Thus, reading internal tracks is carried out with increased, and external - with a reduced number of revolutions. This is the reason for the lower speed of data access for CDs compared to hard disks.

3.2 Media DVD

Universal digital disk   (digitalversatiledisc-DVD) is a kind of drive that, unlike CD, since its introduction into the market has been designed for wide application in both audio-video and computer industry. DVD Discs, having the same size as the standard CD (diameter 120 mm, thickness 1.2 mm), provide up to 17 GB of memory with a transfer speed higher than for a CD-ROM, have access time similar to a CD-ROM, and are shared on four versions:

DVD-5 - single-sided single-layer disc, with a capacity of 4.7 GB;

DVD-9 - a one-sided two-layer disc of 8.5 GB;

DVD-10 - two-sided single-layer disc 9.4 GB;

DVD-18 - capacity up to 17 GB on a two-sided double-layer disc.

DVD - ROM . As for the disc itself, there are few differences between DVD and CD-ROM drives, since the only obvious is the DVD front panel logo. The main difference is that the CD-ROM data is written close to the top layer of the disk surface, and the DVD data level is closer to the middle, so that the disc can be two-sided. Therefore, the optical drive reading unit of the DVD-ROM drive is more complex than its analog for a CD-ROM, in order to create the ability to read both one and the other of these types of media.

One of the earliest solutions was to use a pair of rotary lenses: one for focusing the beam on DVD data levels and the other for reading conventional CDs. Subsequently, more sophisticated designs have emerged that eliminate the need to switch the lens. For example, the "double discrete optical sample" proposed by Sony has separate lasers optimized for CD (wavelength 780 nm) and DVD (650 nm). Panasonic devices switch laser beams with a holographic optical element capable of focusing the beam at two different discrete points.

DVD-ROM drives are much slower than their CD-ROM counterparts. However, since DVD data is packed much more densely, its performance is significantly higher than that of CD-ROMs at the same speed. While a normal CD-ROM audio disc (lx or single) has a maximum data transfer rate of 150 KB / s, a DVD (1x) drive can transmit data at 1250 KB / s, which is only achieved with an eight-fold (8X) CD-ROM drive speed .

There is no generally accepted terminology for describing the various "generations" of DVD drives. However, the term "second generation" (or DVDII) usually refers to 2 high-speed drives, which is also capable of reading CD-R / CD-RW media, and the term "third generation" (or DVDIII) usually means 5-speed drives (or sometimes 4 , 8x, or 6x), some of which are capable of reading DVD-RAM media.

Recordable disc formats DVD

There are several versions of recordable DVDs:

DVD-R-regular, or DVD-R;

DVD-RAM (rewritable);

Recordable DVD .   The DVD-R (or a recordable DVD) is in many respects conceptually similar to the CD-R, it is a once-recorded medium that can contain any type of information normally stored on DVD mass production - video, audio, pictures, data files, programs, multimedia, etc. Depending on the type of information being recorded, DVD-R discs can be used virtually on any compatible device dVD playbackincluding DVD-ROM drives and DVD-video players. Since the DVD format supports two-sided discs, up to 9.4 GB can be saved on a two-way dVD-R disc. The data can be written on DVD with a speed of 1x (11.08 Mbit / s, which is approximately equivalent to the speed of 9x CD-ROM). After recording, the DVD-R discs can be read at the same speeds as the massively reproduced discs, depending on the "x-factor" (speed ratio) of the DVD-ROM drive used.

DVD-R, like CD-R, uses a constant linear velocity (CLV) to maximize the recording density on the disk surface. This requires a change in RPM (rpm), as the diameter of the track changes as you move from one edge of the disk to the other. Recording starts on the inside and ends on the outside. At a speed of 1x, the rotation speed varies from 1623 to 632 rpm for a 3.95 GB disk and from 1475 to 575 rpm for 4.7 GB depending on the position of the recording / reproducing head on the surface. For a 3.95 GB disk, the interval (feed) of tracks, or the distance from the center of one turn of the spiral track to the adjacent part of the track, is 0.8 μm (micron), which is half that of the CD-R. On a 4.7 GB disk, an even smaller track feed of 0.74 μm is used.

DVD - RAM .   A rewritable DVD-ROM or DVD-RAM uses phase-change technology that is not purely optical CD and DVD technology, but a combination of some features of magneto-optical methods and its origin from optical disk systems. The applied format "surface-recess" (landgroove) allows you to record signals both on depressions formed on the disk, and in the intervals between the depressions. Depressions and sector headers are formed on the surface of the disk during its casting.

In mid-1998, the first generation of reusable DVD-RAM capacity of 2.6 GB on both sides of the disk appeared. However, these early devices are incompatible with higher-capacity standards that use the contrast expansion layer and the thermal buffer layer to achieve a higher recording density. Specification for version 2.0 DVD-RAM with a capacity of 4.7 GB on one side was released in October 1999.

DVD - RW .   Known earlier as DVD-R / W or DVD-ER, the DVD-RW media (which became available in late 1999) appears in the evolutionary development of Pioneer's existing CD-RW / DVD-R technologies.

DVD-RW discs use technology to change the phase state of a substance for reading, writing and erasing information. A laser beam with a wavelength of 650 nm heats the sensitive alloy layer to transfer it to either the crystalline (reflecting) state or the amorphous (dark, non-reflective), depending on the temperature level and the subsequent cooling rate. The resulting difference between the recorded dark marks and erased reflections is recognized by the player or the disc drive and allows to reproduce the stored information.

The DVD-RW media uses the same physical addressing scheme as the DVD-R. During recording, the laser of the drive follows the microscopic indentation, recording data in a spiral path.

One of the main advantages of the third rewritable DVD-DVD + RW format is that it provides better compatibility than any of its competitors.

DVD + RW .   The DVD-RAM specification was a compromise between two different offers of the main competitors - the Hitachi group, MatsushitaElectric and Toshiba, on the one hand, and the Sony / Philips alliance on the other.

DVD + RW has much in common with competing DVD-RW technology, because it uses a medium with a phase state change, and assumes a user experience obtained using CD-RWs. In DVD + RW format, discs can be recorded in both constant line speed mode (CLV) for serial video recording and in constant angular velocity (CAV) format for direct access.

DVD + R .   Two-layer system DVD + R uses two thin organic films of the material to be painted, separated by a spacer (filler). Heating by a concentrated laser beam irreversibly changes the physical and chemical structure of each layer so that the changed regions receive optical properties different from the initial ones. This leads to fluctuations in the reflectivity when the disc rotates and creates a read signal the same as in the stamped DVD-ROMs.

Conclusion

Thus, we can draw the following general conclusions:

1. Magnetic storage devices are the most important medium for storing information in a computer and are divided into tape drives (NML) and magnetic disk drives (HDDs).

2. Magnetic disks are used as memory devices that allow storing information for a long time, with the power turned off.

3. The main types of drives: drives on floppy disks (floppy disks); Hard disk drives (HDD); tape drives (NML); CD-ROM, CD-RW, DVD.

4. The main types of media: flexible magnetic disks (Floppy Disk); hard disk drives (Hard Disk); cassettes for streamers and other NML; CD-ROM, CD-R, CD-RW, DVD.

5. There are several versions of recordable DVD: DVD-R ordinary, or DVD-R; DVD-RAM (rewritable); DVD-RW; DVD + RW.

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