Part 6. Peripheral devices

6.1. External memory − magnetic and optical disk drives, flash memory

A disk drive (FDD - Floppy Disk Drive) is a carrier of data, that operates with variable magnetic disks. Floppy magnetic disks (discettes) enable to carry documents and programs from one computer into other, to keep information which is not used in a computer constantly, and do archival copy.

In the personal computers two types of disk drives are used − for a diskette of size 3,5 inch (89 mm) and for a diskette by the size of 5,25 inch (out-of-date model).

In modern computers they use stores for diskettes of size 3,5 inch by a capacity 1,44 Мbyte.

Diskettes are celled in a hard plastic envelope, that considerably increase their reliability and longevity. There is special switch-latch on diskettes, that allows or forbids to conduct a record on a diskette.

Let us consider descriptions of this data carrier.

Capacity. Presently the capacity of diskette 1,44 MByte dissatisfy users. According to modern necessities on software products, that have ten and hundreds megabyte, on such data medium it is possible to carry the small volumes of data only.

Reliability. Comparatively with other data mediums the mechanism of diskette is unreliable enough, as mechanics of disk drive is such, that a head during work touches magnetic surface, damaging it. In addition, a disk surface is badly protected from influence of surrounding envirounment and has electromagnetic instability.

Operating speed. A read/record rate at the use of diskettes presents about 30 ÷ 50 Kb/s comparatively with 20 ÷ 40 Mb/s at a hard disk. Thus, such operating speed extremely unsatisfactory, in consideration of small capacity of carrier.

Price. The cost of disk drive and diskettes is relatively small and, as a result, high availability of users to it as a carrier of data.

Popularity. In spite of that a disk drive is actively used relatively a long ago, it and presently most widespread in the modern personal computers. Many solutions were offered, that tried to force out a disk drive, however deciding this task was not succeeded. To this time such technology of storage of information did not have at the market a competition which would provide more subzero cost of store and data carriers. In addition, obvious advantage is possibility of record which enables to carry information from one computer on other.

The computer-integrated on a system board controller of disk drive (FDC - Floppy Disk Controller) enables to plug in two disk drives.

For pluging of disk drives they apply the special cable which has 34 conductor. A device number is determined on a cable, as two disconnectors of cable unidentical. A device which is connected to the end of cable gets a number 1, and a device which is connected to the middle of cable is a number 2.

For the task solution of providing of greater capacity on one variable carrier (diskette) with acceptable operating speed comparatively with a general disk drive a company IOmega created a store which was named by IOmega Zip 100 Мb.

In this store a diskettes of capacity100 Mb are used, thus for it it is impossible to insert ordinary diskettes, but only special diameter 3,5 inches and in thick about 9 mm.

Instead of Zip100 began to produce the new model − Zip250 Мb, that operates as with diskettes 250 Mb, so with diskettes 100 Mb. This store operates practically with any interface: IDE, LPT, USB. Basic advantages are − simplicity of setting and exploitation and not-difficult software, proper operating speed. However operating speed belongs only to the internal models or models with interface USB, a device with the interface LPT is limited to the productivity of parallel port oneself. Basic defects are − repugnance with ordinary diskettes and not very much high reliability of device.

Flash-memory. Lately flash-memory is used not only as internal memory but also as external, that connected to the computer through the interface USB. Such device can be switched on and off without the restart of computer. A device has: microcircuits of flash -memory, controller which manages access to the microcircuits, adapter USB.

Devices have small sizes, different forms of corps, that manufactured from a plastic or aluminium. During access to them an indicator lights up. Permission or prohibition of read-out is realized by a switch with the use of password. A device can be used as loadable. Basic properties of external storage such: appropriate capacity (16, 32, 64, 128, 256, 512 Mb or 1, 2, 4 Gb), speed of data transfer, reliability.

Maximal speed of data transfer for devices reaches 1,5 Mb/s (USB 1.1) and 50,60 Mb/s for USB 2.0. Duration of data retention about 10 years, the amount of rewriting cycles reaches 1 million.

Flash-memory is used not only in computers, but in mobile telephones, network equipment, printers, faxes and others like that. Microcircuits are produced by all producers of memory microcircuits. Such microcircuits have built-in electric circuits which enable to generate a discharg for erase of data or on all microcircuit, or on some its areas − blocks and provide access to data of short duration.

In some devices it is possible connection of flash-disk, player with reiteration functions, digital dictaphone and FМ-radio.

So, a basic problem is providing of adequate tools of delivery and distribution of information. Carriers must contain the enormous volumes of different information, allow fast access to some its components, their high-quality recreation, and here to be cheap, compact and reliable. This problem was solved after appearance of optical disks of different types.

Presently there are three types of technology of optical memory. The first type − it is a disk drive ROM on a compact disk (СD - RОМ) named so because it uses optical disks according to sample optical disks in stereo sound systems, and functionally corresponds to the permanent memory. The second type − disk drive WORM (Write Once, Read Мany times) a record is possible only one time, but reading of data is frequent. The third type has many names − optical with rewriting, optical with erase of information, magnetically-optical.

СD - RОМ (Сompact Disk Read Оnly Меmогу) − optical disk, which consists of thin aluminium tape, covered by the protective layer of polymer. Record of information on СD - RОМ takes place during its making, by means of punching, as a result in an aluminium layer a picture is created from hollows due to which the code of information is carried out. At the read-out of СD in the special device which is called by СD - RОМ - Drive, the surface of aluminium is scanned by a laser ray, and then laser light is analysed, reflected from the surface of disk, whereupon the picture of hollows on a disk is restored and thus written information is read.

СD - RОМ − round disk by diameter 120 mm with the central opening by diameter 15 mm, thickness 1,2 mm. The central area round opening by a width 6 mm is called a fastening area (clamping area). After it directly there is title part (lead in area) which contains maintenance of disk (table of content). After title part the area is placed in a width a 33 mm, intended for storage of data. Physically it is only track. Finishing is a terminal area (lead out) in a width a 1 mm. External dinner of disk has a width a 3 mm.

СD – RОМ are made by the method of punching. At first make plastic basis from the transparent plastic or polycarbonate, whereupon over a plastic for the reflection of laser ray they spread the layer of aluminium, which, in turn, is covered by the protective layer of varnish. One can see this argenteum well from the back of transparent disk.

The area of data storage contains from 1 to 99 tracks usually, but placing different information on one track is not allowed. Digit information is saved on СD - RОМ as microscopic hollows − pits, which are alternated downstep of spiral.

Typical length of pit presents 0,8 ÷ 3,2 μm, width − 0,6, depth − 0,12, and distance between the separate paths − 1,6 μm. On one inch (2,54 cm) of disk surface 16 thousand or 625 turns take place on one millimetre (for comparison on one inch of magnetic disk 96 paths are contained only). Due to such small values of pits a СD - RОМ contains the enormous volume of information − about 700 Mb. The new types of disks have on an order a greater volume and feasible record of information by an user. The read-out of СD is carried out in a special device which is called by СD - ROM - Drive.

It is known that most stores are external and built-in (internal). Most stores of offered presently СD - ROM are built-in.

On the front panel of every store there is access to the mechanism of loading of compact disk. One of most widespread there is a mechanism of СD - ROM loading by means of caddy − plastic container in which they lay a compact disk before loading direct in a drive. Another way of loading − by means of tray-mechanism, which similar to the tray which is pulled out from a store usually after pressure of the button "Еject". On it they set a compact disk, whereupon they push tray-mechanism in a store by hand. There are varieties of tray-mechanism, for example рор-uр. In this case loading of disk is semi-automatic and place is taken after an easy touch.

In addition, on the front panel of drive it is placed: indicator of device operation (busy), nest for connecting of earphones or stereo sound system (for listening of audiodisks), automatic fader (also for аудіоCD). For the system of саddy the opening is foreseen also by means of which it is possible to fish out a compact disk even in an emergency situation, for example, if the button of "Еject" malfunctions.

On the backplane of almost all drivers of СD - RОМ there are usually three disconnectors: interface, feed and audio. In particular, a disconnector for the leadingout of voice signals enables to connect a driver to a sound card.

Except these disconnectors in case of the use of SCSI-interface there is a set of jumpers or switches on the backplane of drive which determine a device number and its operation mode.

Typical device of store СD-RОМ Drive is represented on fig. 6.1. In the drive of compact disks there are a few base elements - laser diode, servomotor, optical system, photodetector.

Operating principle of disk drive is similar to operating principle of ordinary disk drives for floppy disks.

Fig. 6.1. Typical device of store CD-ROM Drive

Semiconductor laser 4 generates a low-powered laser ray which gets on reflecting mirror.

Motor, controlled by microprocessor СD-RОМ Drive displaces a movable carriage 6 with a mirror and lens 7 to the necessary path of compact disk 1. The ray of laser focuses on the surface of СD-RОМ by means of lens which focuses a reflected from the surface of disk ray. This ray by means of the optical system 5 is delivered on a detector 2, which converts the accepted light pulses into electric, which are then decoded by a controller 3 and transfered to the computer as digital data.

So, the read-out of information from a disk takes place due to login of intensity change of reflected emission from the aluminium layer of low-powered laser. If a ray gets in pit, it disperses, and only small part of emission is reflected back and comes to the photosensitive diode. On a diode light impulses transform in electric, in particular, bright emission is converted into zero, and weak − into unit. Thus, pits are interpreted by a disk drive as logical zeros, and smooth surface − as logical units.

The surface of optical disk (СD-RОМ) moves relatively lazer head with permanent linear speed (СLV, Сопstant Linear Velocity), and an angular speed changes depending on radial position of head. Yes, reading of internal sectors is carried out with accelerated, and external − with the diminished number of turns. That is why a speed of access to CD data is less than, for example, with winchesters.

Basic properties of СD-RОМ, as data storage, are such.

Productivity of almost any device of data storage it is possible to describe by two major parameters − duration of access and speed of linear read-out. Duration of access is determined by rotation speed of compact disk and by the rate of movement of read-out head. Speed of access (ассеss time) determines mean time (ms), necessary for an exposure and loading of the first block of data in an internal buffer. The standard of МРС1 sets such time −1s or less than, but most modern drives have speed of access 50 ÷ 80 ms. Clearly, that this parameter does not include time, necessary for the running of motor at operating condition.

Speed of data transfer (dats-transfer rate) depends on two factors − data density and speed of disk rotation. The data density – it is the amount of bits (pits) on an inch (or millimetre). Yes, for 16-bit stereosignal of quality аudio-СD (frequency 44,1 kHz) speed must be 1,4 Мb/s. Dividing this value by the number of bits in a byte (8), will get 176,4 Kb/s − mean value for data transfer speed. Standard МСР 1 determines data transfer speed 150 Kb/s. Producers measure read-out speed of СD-RОМ Drive by numbers, multiple to this minimum speed. For example, if speech goes about the four-speed device of read-out of disks (4х), then it means that such СD-RОМ Drive can provide speed of read-out from a disk 150 Kb/s ∙ 4 = 600 Kb/s. Presently mostly use disks with speeds of 40х ÷ 50х.

Reliability. It is known that at first СD developed for storage of music records. If at the recreation of music from a compact disk the incorrect read-out of one bit will take place, then it in any way will not influence on quality of recreation. Therefore on disks with the music records it is provided less of measures in relation for providing of read-out reliability. If a disk is processed with data, then an incorrect read-out even of one bit will result in complete uselessness of finding. Therefore on a disk with data, except useful information, they write down surplus (superfluous) data by means of which in case of uncertain reading of any information content it is possible to restore it. Yes, on СD there are very powerful codes of error correction, which enable to restore about 1000 (!) bits which unright go in succession. For example, if on a disk is written music, then size of block of 2352 bytes fully used for storage of musical data, and if the data written on a disk, then only a 2048 byte is used actually for data storage, and other 304 bytes are used for official necessities, in particular a 288 byte for the special redundant code of error correction.

Except such programmatic defence which presents the about 1/6 useful capacities of disk, a disk is protected yet by polymeric tape. On the whole СD can be considered the reliable enough carrier of data, but it needs the enough careful use: it follows to protect a disk surface from scratches and mechanical damages.

Size of buffer. For the increase of the disk drives productivity they are supplied with buffer memory. A buffer of disk drive is memory for data short-term storage after the read-out of them from СD-RОМ, but yet before transfer in controller. Such buffering enables to the disk device to pass data to the processor by small portions, but not to occupy its time by the slow transfer of permanent data flow. The standard МРС sets the buffer size 64 Kb, and it in a buffer will be about 0,4 s of 16-bit stereosignal as СD-Аudio with frequency 44,1 kHz. For speed devices the size of buffer can reach 256 Kb and even 1 Mb.

Capacity and price. Comparatively with a diskette, a compact disk has a considerably higher capacity: 650 Mb. Such capacity predetermines application of compact disk as a data carrier for different installative distributive packages for storage of which before applied diskettes. It is assisted by the subzero cost of СD-RОМ Drive, which presently is inalienable component of any PC and subzero cost of carrier СD-RОМ.

Devices for a record on СD. Devices which enable to conduct a record on laser disks name СD-R Drive (СD Recordable), and disk which a record is done on, − СD-R. Clean СD-R has not a single deepening on the surface. During a record on the disk surface the laser ray of recoder burns out deepening, realizing thus record of information. Clearly, that, writing down information on such disk, it can not be erased or changed. Speed of devices is usually marked by two numbers, for example 4х/24х, id est record is carried out on speed 4х, and a read-out − on 24х.

Except СD-R with a single record there are devices for a frequent record and erase of information − СD-RW (СD RеWritable). Disk СD-RW has an active layer of the alloy Аg − Іn − Sb − Te. Layer of such alloy at heating to 500 ÷ 700 °С is melted, losing a reflection property, and it is thus possible to record a new information. After heating to the temperature about 200 °С property of layer are restored, thus, record on such carrier it is possible to do repeatedly. Accordingly, devices for a record on СD-RW can yet write down the gold disks СD-R and to read ordinary СD-RОМ. Device is marked by three speeds, for example, 4х/10х/32х, that means rewrite on speed 4х, record on СD-R on speed 10х, read-out on speed 32х. СD-RW have large prospects. Yes, at the acceptable price of device, it is, at first, good device for information storage, and, secondly, − universal method of information transfer.

DVD - discs. The future of compact disks − is a digital universal disk, so-called DVD (Digital Versatile Disc). It is a new standard which increases the volume of memory considerably. Main problem of modern technology of СD-RОМ consists in that it is hardly limited by the size of disk memory. Disk СD-RОМ can contain 650 Mb of data maximally, and although it is a very large volume, but it is not enough to solve many tasks, especially for those, which use video.

Specification of DVD. In accordance with the standard DVD-disk is a single-sided, single-layer and contains 4,7 Gb of information.

A new disk has the same diameter, as modern compact disks, but it is twice more thin (0,6 mm). DVD-disks keep data also in a shape of microscopic deepening, minimum length of which presents 0,4 μm. In addition, a spiral path in the disks of DVD has a step of 0,74 μm. For the read-out of information from DVD a red laser is used of lengh wave 635 ÷ 650 nm. Diminishing of sizes of deepening and step of spiral path assisted the increase of disks capacity of almost seven times.

Applying a compression by the standard МРЕG - 2, on a new disk it is possible to place 135 min video, id est a full-length film is with the complete amount of frames, with three channels of high-quality sound and four channels of sub-title. The value of disk capacity is not random, as it was created for the use in film industry which required inexpensive and reliable replacement of video cassettes a long ago. In a store DVD a laser is used with a less wave-length, which enables to read considerably short strokes.

Most disks of DVD have a capacity 4,7 Gb. Application of doubling density charts and their combining, enables to have disks of greater capacity: from 8,5 and 9,4 Gb to 17 Gb. Such structural types of DVD are known.

Single Side/Single Layer: it is a simplest structure of DVD-disk. On such disk it is possible to place to 4,7 Gb of data, in particular this capacity more than capacity of ordinary sound СD and СD-RОМ-disks in 7 times.

Single Side /Dual Layer: this type of disks has two layers of data, one of which semitransparent. Both layers are readen from one side and on such disk it is possible to place 8,5 Gb of data, id est on 3,5 Gb more than on the sigle-sided/single-layer disk.

Double Side/Single Layer: on such disk 9,4 Gb of data (for 4,7 Gb on every side) are placed.

Double Side/Double Layer: structure of this disk provides possibility to place to 17 Gb of data (for 8,5 Gb on every side) on it.

Nine companies which presently lead in development of new generations of DVD-technologies, − Ніtасhі, LG Еlectronics, Маtsushita Еlесtгіс, Ріоnеег Соrрогаtіоn, Rоуаl Рhіlірs Еlесtгоnісs, Sаmsung Еlесtгоnісs, Shаrp Соrроrаtіоn, Sоnу and Тhоmsоn Мultіmеdіа announced the new format of recoding of optical disks for video.

This format has the name "Вlu-rау Dіsс". The name of technology was given after length by the laser radiations − blue-violet, which will apply during work with new disks. New disks of standard of Вlu-rау Dіsс, as well as present СD/DVD carriers, have a diameter 120 mm. Disks of Вlu-rау enable to write down on every side about 50 Gb of data at the use of laser with the wave-length of 405 nm. Yes, a firm Тоshiba produced bilateral DVD of capacity 110 Gb.

It should be noted that the devices of DVD differ in read-out speed of data. Standard speed − is 1,3 Mb/s, that approximately equivalence to the store of СD-RОМ 9х. Duration of access equals about 100 ÷ 150 ms. Presently there are stores DVD 16х. Such carriers fully pin-compatible with previous standard, can read-out data from ordinary СD-RОМ and to play back audiodisks.

Connecting of СD-RОМ, СD-R, СD-RW, DVD-RОМ. All enumerated devices connect like a hard disk. They keep up the same modes of РІО 1,2,3,4, UDMA 33,66,100.

Lately most widespread are SСSІ and IDЕ interfaces. In turn, both interfaces SСSІ and IDЕ have the improved versions. For SСSІ − this SСSІ - 2 and Fast SСSІ - 2, for IDE there is interface of EIDE.

There are a few methods of connecting of disk drives of СD-RОМ. The first method is based on that one channel of interface IDE can keep up two built-in devices. Store СD-RОМ connect to the input-output board through the interface IDE together with hard disk by principle master/slave. However in this case speed of data exchange goes down with a hard disk. One of methods of this problem solving there is connecting of devices СD-RОМ to the different channels of one interface ЕIDE or to two different contrpllers IDE. For connecting of these devices apply the same 40-pin (40-or 80-conductor) cables.

If СD-RОМ has SСSІ interface, then it accordingly plug in to SСSІ of controller. Other approach is application of 32-bit drivers of disk drives СD-RОМ instead of 16-bit. There is also possibility of connecting of disk drives СD-RОМ through controller of sound card. However one cannot to forget that modern system boards can contain the built-in controllers SСSІ and IDE, that in general eliminates a requirement in the additional input-output board for connecting of disk drives СD-RОМ.