Optical disk is a collective name for storage media made in the form of disks, read from which is carried out using optical radiation.
History The first optical discs were developed at the turn of the 70s and 80s by the joint efforts of Sony and Phillips. &
History of CD (Compact disc) Mini. Disk (MD) DVD (Digital Versatile Disc) HD DVD & Blu-ray (BD) HVD (Holographic Versatile Disc)
Structure of a CD - The disk is usually flat, its base is made of polycarbonate, on which a special layer is applied, which serves to store information. - CD diameter 120 mm. - Disc thickness 1.2 mm.
Write-once discs (CD-R). A write-once disc consists of active, reflective and protective layers, which are sequentially applied to a polycarbonate base.
Principle of CD-R recording During recording, a powerful laser beam heats small areas of the active layer. Under the influence of high temperature, the properties of the substance of the recording layer in the place of heating change, as a result, it ceases to transmit light.
Principle of CD-R recording It is impossible to restore the transparency of the substances used as the active layer in CD-R discs. Damage the recording on active layer, there is only one way - to make transparent areas opaque.
Reusable discs (CD-RW) The difference between such discs and CD-Rs lies in the design of the recording layer. The intermediate layer of special organic material can be either amorphous or crystalline. Recording laser beam
CD-RW Amorphous substances tend to crystallize over time. No matter how we store a CD-RW, after a few years the recording will be irretrievably lost. In addition, such discs can easily be erased by simple heating. !
Structure DVD discs The principle of burning a DVD is not much different from the principle of burning a CD. The basis for recording and storing data on DVD-RAM and DVD-RW discs is the technology of changing the phase state of matter. The layer-by-layer structure of one half of the disk is shown in the figure.
Principle of DVD recording The recording of amorphous areas is shown in this graph. A short, high-power laser pulse melts the recording material. This is followed by cooling below the crystallization temperature. The result of cooling is to prevent the formation of crystallization centers. Thus, the growth of the crystalline phase does not occur, and the substance remains in an amorphous state.
Erasing from a DVD To erase, you need to return the substance to its crystalline state. Again, using a laser, the amorphous substance is heated to temperature T. Heating (or rather, annealing) continues for a time sufficient to restore the crystalline state of the substance. This time must be longer than the so-called crystallization time.
Writing DVDs When writing discs, a multi-pulse recording strategy is used. Each recordable mark is formed using powerful laser pulses. . After each pulse, the molten material cools, forming an area with an amorphous phase.
Burning discs at home To burn discs at home, you need not only a CD burner, but also special software.
Recording a disc at home The process of recording one session is a single operation that cannot be interrupted, otherwise the disc will be damaged.
Recording a disc at home Before you start recording, you need to create full list files included in the session; Subsequent addition of files to disk is possible only in the form of additional sessions.
Recording a disc at home CD-ROM drives, which do not support multi-session recording, read only the first TOC from the disk - accordingly, they can only be used to read files from the first session.
Label technology. Flash Labelflash is a technology that allows you to apply your drawings to recordable DVDs. It was introduced by NEC in December 2005.
How Label works. Flash To create a picture, a different type of dye is used, which provides greater image contrast.
Ministry of Education of the Russian Federation
Irkutsk State Technical University
Department of AS
Course work
“CDs. Classification. Reading and writing principles»
Completed: art. gr. ASU-99-1
Belyaev V. A.
Accepted by: Bakhvalov S.V.
Irkutsk, 2002
General information about CDs………………3
CD format……………………………4
Classification………………………………….5
Principle of CD-R recording…………………………….6
CD-RW recording principle………………………….7
Recording methods…………………………………8
Literature……………………………………………………11
In 1982, Sony and Philips completed work on the CD audio format (Compact Disk), thereby ushering in the era of digital media on compact discs. The operating principle of these discs is optical. Reading and writing is carried out by a laser. In a CD, data is encoded and recorded as a sequence of reflective and non-reflective sections. The reflection is interpreted as one, the “valley” as zero. I will give some technical parameters of CDs. The operating wavelength of the laser is 780 nm. CD diameter 120 mm. Disc thickness 1.2 mm. Disc capacity 680 MB (74 min audio). Weight 14-33 g. The chain of pits is arranged in a spiral, like in a gramophone record, but away from the center (in fact, a CD is a sequential access device with fast rewinding). The interval between turns is 1.6 µm, pit width is 0.5 µm, depth is 0.125 µm (1/4 wavelength of the laser beam in polycarbonate), minimum length is 0.83 µm (Fig. 1).
Rice. 1. CD surface.
There are modifications of 80 minutes (700 MB), 90 minutes (791 MB) and 99 minutes (870 MB). Nominal (1x) data transfer rate is 150 KB/sec (176400 bytes/sec audio or “raw” data, 4.3 Mbit/sec “physical” data). While all magnetic disks rotate at a constant number of revolutions per minute, that is, with a constant angular velocity (CAV, Constant Angular Velocity), a compact disk usually rotates at a variable angular velocity to provide a constant linear speed when reading (CLV, Constant Linear Velocity). Thus, reading the internal sides is carried out with an increased number of revolutions, and the external ones - with a reduced number of revolutions. This is what determines the rather low data access speed for CDs compared, for example, with hard drives.
Consider the CD format.
The surface of the disk is divided into areas:
PCA (Power Calibration Area). Used to adjust the laser power of the recording device. 100 elements.
PMA (Program Memory Area). The coordinates of the beginning and end of each track are temporarily recorded here when the disc is removed from the recording device without closing the session. 100 elements.
Lead-in Area - a 4 mm wide ring (diameter 46-50 mm) closer to the center of the disk (up to 4500 sectors, 1 minute, 9 MB). Consists of 1 track (Lead-in Track). Contains TOC (absolute temporary addresses of tracks and the beginning of the output area, accuracy - 1 second).
Data area (program area, user data area).
Lead-out area - ring 116-117 mm (6750 sectors, 1.5 minutes, 13.5 MB). Consists of 1 track (Lead-out Track).
Each byte of data (8 bits) is encoded into a 14-bit character on the medium (EFM encoding). Characters are separated by 3-bit spaces, chosen so that there are no more than 10 consecutive zeros on the medium.
From 24 bytes of data (192 bits) a frame (F1-frame) is formed, 588 bits of media, not counting the spaces:
synchronization (24 bit media)
subcode symbol (bits of subchannels P, Q, R, S, T, U, V, W)
12 data characters
4 character verification code
12 data characters
4 character verification code
Decoding may use different strategies for detecting and correcting group errors (probability of detection vs. reliability of correction).
A sequence of 98 frames forms a sector (2352 information bytes). The frames in the sector are shuffled to reduce the impact of media defects. Sector addressing originates from audio discs and is written in A-Time format - mm:ss:ff (minutes:seconds:beats, fractions per second from 0 to 74). The countdown starts from the beginning of the program area, i.e. the sector addresses of the input area are negative. The subchannel bits are assembled into 98-bit words for each subchannel (of which 2 bits are synchronization). Subchannels used:
number of channels
data or sound
is it possible to copy
a sign of frequency pre-emphasis: artificial increase in high frequencies by 20 dB
subchannel usage mode
q-Mode 1: The input area stores the TOC here, the program area stores track numbers, addresses, indexes and pauses
q-Mode 2: disk catalog number (same as on the barcode) - 13 digits in BCD format (MCN, ENA/UPC EAN)
q-Mode 3: ISRC (International Standard Recording Code) - code of the country, owner, year and serial number of record
P - marking the end of the track (min 150 sectors) and the beginning of the next (min 150 sectors).
Q - additional information about the track contents:
A sequence of sectors of the same format is combined into a track (track) from 300 sectors (4 seconds, see subchannel P) to the entire disc. A disc can have up to 99 tracks (numbered 1 to 99). A track may contain service areas:
pause - only subchannel information, no user data
pre-gap - the beginning of the track, does not contain user data and consists of two intervals: the first, at least 1 second long (75 sectors), allows you to “build up” from the previous track, the second, at least 2 seconds long, sets the format of the track sectors
post-gap - end of track, does not contain user data, at least 2 seconds long
The lead-in digital area must end with a post-gap. The first digital track must start from the second part of the pre-gap. The last digital track must end with a post-gap. The output digital area does not contain pre-gap.
There are many standards and formats for CDs, depending on the purpose and manufacturers. I will give as an example not all existing ones: Audio CD (CD-DA), CD-ROM (ISO 9660, mode 1 & mode 2), Mixed-mode CD, CD-ROM XA (CD-ROM eXtended Architecture, mode 2, form 1 & form 2), Video CD, CD-I (CD-Interactive), CD-I-Ready, CD-Bridge, Photo CD (single & multi-session), Karaoke CD, CD-G, CD-Extra, I -Trax, Enhanced CD (CD Plus), Multi-session CD, CD-Text, CD-WO (Write-Once). A full description of them would take too much space, and this is not the purpose of writing this work.
Depending on the number of possible recording operations, CDs are divided into: CD-ROM (read only memory), CD-R (recordable), also known as CD-WORM (write once read many), CD-RW (rewritable). Accordingly, the CD-ROM is manufactured at the factory, and further recording on it is impossible; CD-R is intended to be written once at home; CD-RW allows many write operations. CD-ROM discs are polycarbonate, coated on one side with a reflective layer (aluminum or - for critical applications - gold) and a protective varnish on the other. The reflectivity is changed by stamping recesses in the metal layer. At the factory they are simply stamped from the matrix. This is not very interesting for us, and we will dwell in more detail on discs that can be recorded on a home computer.
Let's start with write-once discs (CD-Rs).
In terms of its internal structure, a CD-R disc resembles a layer cake, the “filling” of which consists of active, reflective and protective layers, which are successively applied to a polycarbonate base.
At the same time, the basis of a CD-R disc is no different from that used in the technology of manufacturing compact discs by casting: the characteristics of the plastic must be such that the laser beam passing through it is properly focused and does not cause destruction of the disc. An active (or recording) layer is applied to the base, on which, in fact, information is recorded. During recording, a powerful laser beam heats small areas of the active layer. Under the influence of high temperature, the properties of the substance of the recording layer in the place of heating change, as a result, it ceases to transmit light. In other places that were not heated by the laser, light still passes through the recording layer unhindered. Cyanine and phthalocyanine are commonly used as materials for the recording layer.
All that remains is to deal with the reflective layer. So, the reflective layer is the thinnest plate of gold or silver. Moreover, silver is better because it has a higher reflection coefficient. But, nevertheless, discs with a gold reflective layer continue to be produced, although they are worse and much more expensive. As usual, you have to sacrifice one quality for the sake of another: gold is a very durable material, and silver oxidizes over time. Therefore, in cases where long-term data storage is required, disks with a gold reflective layer are used. Well, the last layer, protective, is applied on top of the reflective one and serves to mechanically protect the CD-R disc and apply a label to it. Here, too, options are possible: in the simplest case, the protective layer is a varnish coating. Not the best protection option. The varnish can peel off, and, even worse, there may be a chemical reaction between the varnish and various substances that come into contact with it (for example, with the ink you use to write on the back of the disc). However, recently some manufacturers of CD-R discs have been using special resistant varnishes to coat discs, which gives them additional reliability. More reliable protective coatings are an additional layer of special plastic. In addition to protection, this method also makes the appearance of the disc more attractive compared to varnish.
It is impossible to restore the transparency of substances used as the active layer in CD-R discs. On the one hand, this provides some guarantee that the recorded information will be securely stored. Indeed, there is only one way to damage the recording applied to the active layer - to make the transparent areas opaque. This is what can happen under the influence of, for example, bright sunlight. On the other hand, it is impossible to rewrite a disc once written. Unfortunately, it has not yet been possible to resolve this contradiction. Today we are forced to choose between the possibility of rewriting and the reliability of information storage.
And if we choose to rewrite, we will have to use a CD-RW disc. The only difference between such discs and CD-Rs is the design of the recording layer. For CD-R discs, recording is based on changes in the optical properties of the layer under the influence of temperature - when heated, the layer becomes cloudy. The principle of recording CD-RW discs is a little more complicated; it uses the phenomenon of phase transition. The intermediate layer of special organic material can be either amorphous or crystalline.
An amorphous substance, as is known from a physics course, is a substance that, when heated, does not turn into a liquid, but gradually softens and becomes more and more fluid. An example of such a substance would be the well-known plasticine. Or honey. By the way, the example of honey clearly shows the general property of amorphous substances - over time they turn into a crystalline form. Place a jar of transparent fresh honey in the cupboard and do not touch it for 2 years. Then take it out, and you will see that the honey has thickened, or even become solid, “candied.” And it became opaque! This is the principle on which CD-RW recording is based. The transparency of the CD-RW recording layer depends on the state in which the substance is, amorphous or crystalline. And we can control the process of transition from one state to another. If the recording layer is heated to a sufficiently high temperature and then cooled sharply, the substance turns into an amorphous form. This is exactly how the recording process works. On a blank CD-RW disc, the recording layer is in crystalline form. A powerful beam from a recording laser heats up a section of the surface and turns off, the disk quickly cools down and at this point part of the active layer turns into an amorphous form. In order to return the substance of the active layer to the crystalline state, it is heated again, but to a lower temperature (with a less intense beam). And the substance returns to the crystalline state. This operation can be performed about 1000 times, which is how many rewrite cycles CD-RW discs can withstand.
And everything would be fine if it were not for the very peculiarity of amorphous substances to crystallize over time. No matter how we store a CD-RW, after a few years the recording will be irretrievably lost. In addition, such discs can easily be erased by simple heating. But you can re-record.
Another feature of CD-RW discs appears when reading. If in CD and CD-R discs we clearly distinguished two types of surface areas - light reflecting and non-reflecting, then in CD-RW the entire surface is reflective, although to varying degrees. Therefore, when reading a CD-RW disc, information is read at the moment when the laser beam hits the transition area between crystalline and amorphous matter. The laser used in this entire process is standard, with a wavelength of 780 nanometers. Reading is also done with a standard laser, but the difference in signal levels is less for CD-RW discs than for CD-ROMs.
Rice. 2. Structure of CD, CD-R, CD-RW discs
Let's look at ways to burn CDs at home. To do this, you need not only a CD burner, but also special software. They are usually supplied together. Examples of such programs are Easy CD, CD Creator, CD Publisher. The Windows XP operating system has built-in support for burning CDs.
The process of recording one session is a single operation that cannot be interrupted, otherwise the disc will be damaged. To ensure uniform flow of recorded information to the laser, all drives have a buffer, the exhaustion of data in which (Underrun) leads to an emergency interruption of recording. Exhaustion of data in the buffer can be caused by the launch of parallel processes, the operation of the virtual memory system (swapping), hijacking of the processor by “rogue” device drivers, or freezing of the program or operating system. Mechanical shocks from the drive also cause recording failure.
There are two main CD-R recording modes: DAO (Disk At Once - the entire disc at one time) and TAO (Track At Once - one track (session) at one time). When recording using the TAO method, the laser is turned on at the beginning of each track and turned off at the end; At the points where the laser is turned on and off, a series of special frames are formed - run-in, run-out and link, designed to link the tracks together. A standard interval contains 150 such frames (2 seconds). When recording using the DAO method, the laser is on throughout the recording of the entire disc.
A disc written in one go is the most universal and can be read by any CD-ROM with any file manager, however, after writing, it is impossible to add new data to the disc, and the DAO mode is not supported by all recording drives. This mode is also desirable for recording master discs for subsequent duplication by stamping - most standard machines for making matrixes accept only continuously recorded originals.
In TAO mode, multi-session discs are written that allow subsequent data recording; in this case, only the Lead In zone (open session) is recorded for the session. When recording each subsequent session, the previous one is closed by recording the Lead Out zone followed by the Lead In of the new session. These two zones consume an additional 13.5 MB (6750 frames) of disk space.
According to the standard, in order to be read normally in all devices, the disk must be Closed by writing the output zone. Closing the disk increases the likelihood of it being successfully read in other drives (the vast majority of modern drives do not pay attention to whether the disk is closed), but makes it impossible to add additional sessions.
Before you start recording, you need to create a complete list of files included in the session; Subsequent addition of files to the disk is possible only in the form of additional sessions. CD-ROM drives that do not support multi-session recording read only the first TOC from the disk - accordingly, they can only read files from the first session. Multi-session CD-ROMs only read the latest TOC, so the last TOC on a multi-session disc must also contain references to files from previous sessions. To do this, when recording the next session, use the option of importing sessions (Import Track) to create a complete overall TOC. Directories with the same names are merged, as when appending to a regular disk. In any case, files are addressed within the entire disk, so only TOCs are merged. Session files that were not imported when creating the next one will not be present in the resulting directory and normal access to them will be impossible, however, many CD-R burning programs allow you to selectively read individual disc sessions. If recording to a one-time multi-session disk is interrupted for some reason, in some cases it is possible to use the remaining free disk space. This requires a recording program that has an option to close a session (Close Track/Session), after which the necessary data is recorded in the next session without importing the interrupted session (preceding sessions can be imported).
Because the final visibility of each file is determined by the TOC import process, it is possible to exclude individual files from the catalog and selectively replace files with matching names. The old copy of the file continues to remain on disk in one of the previous sessions, but a link to the new copy is placed in the new directory. Selectively excluding files from previous sessions into the new session's directory has the effect of "deleting" them. The visibility of files "deleted" in this way can later be "restored" by importing them into new sessions.
To record CD-RWs, they can be pre-formatted - divided into sectors, like magnetic disks. After formatting, a CD-RW disk can be used like a regular removable disk - standard file operations of copying, deleting and renaming are converted by the CD-RW drive driver into a series of disk sector rewrite operations. Thanks to this, no special software is required to work with CD-RW discs, except for a drive driver with UDF support and an initial partitioning program.
Some versions of burning software allow you to burn bootable discs. The bootable part of the CD-ROM is recorded as an image of a boot floppy disk or hard drive, from which the A: drive is emulated when the motherboard BIOS boots.
Literature
people.kstu.edu/CSN/CDR/rab.htm
kstu.kz/~yas/theory_lw/opt_70.htm
bog.pp/hard/cdrom.html
Similar abstracts:
The presence of an active (recording) layer in CD-R(blank for recording). Exact values for the width, depth and angle of the side walls. Required laser power when recording. Types of dyes, reflective, protective and decorative layers of a compact disc.
In the first hard models, a material based on iron oxide was used as a magnetic coating. Now manufacturers use chromium oxide, which has greater wear resistance.
How a CD-ROM drive works The operating principle of a CD-ROM drive is similar to that of conventional floppy disk drives. The surface of the optical disk (CD-ROM) moves relative to the laser head at a constant linear speed, and the angular speed varies depending on the radial position...
A typical CD-ROM drive consists of a printed circuit board with electronics, a spindle motor, a readout system with an optical head, a CD loading system and a frame movement mechanism with drive mechanics. The electronics board contains:
All drive operation control circuits;
Interface connector for connecting to a computer;
Analog sound output(Analog Audio);
Digital audio output S/PDIF (Digital Audio - may not be available on some models).
The spindle motor is used to rotate the disk at a constant linear (CLV - Constant Linear Velocity) or angular (CAV - Constant Angular Velocity) speed. Maintaining a constant linear speed requires changing the angular speed of the disk depending on the position of the optical head.
A stand is attached to the axis of the spindle motor, against which the bottom side of the disk is pressed (for horizontal loading). A magnetized metal tip having a cone shape is attached to the end of the spindle motor axis. On the other side of the disk - the upper side in the case of horizontal loading, that is, above the disk - there is a magnetized flywheel, which attracts the metal tip, as a result of which the disk is sandwiched between the stand and the flywheel, which ensures vertical fixation of the disk and good adhesion of the disk to the rotating stand while the drive is running.
The reading system consists of an optical head and a mechanism for its positioning. The head contains a laser emitter based on an infrared laser LED with a wavelength from 770 to 830 nm (usually about 780 nm) and a power of 0.2-0.5 mW, a laser beam focusing system, a photodetector and a pre-amplifier. The focusing system is a set of moving lenses driven by an electromagnetic “voice coil” system, similar to a moving loudspeaker system. Changing the magnetic field strength causes the lenses to move and the focus point of the laser beam to move.
Due to its low inertia, such a system effectively tracks the vertical runout of the disk even at significant rotation speeds. The optical head positioning mechanism has its own motor, which drives the carriage with the optical head using a gear or worm gear.
There are three types of disk loading system:
Caddy - using a special case for the disk, inserted into the drive receiving hole;
Tray - using a pull-out tray on which the disc is placed;
In Caddy and Slot-in drives, the disk can be loaded both horizontally and vertically - that is, when the drive is mounted horizontally and, accordingly, vertically.
After loading, the disc does not touch any parts of the drive, except for the stand and the flywheel, after which it can already be untwisted.
The front panel of the drive usually contains:
Eject button for loading/unloading a disc;
Disk access indicator Busy (in some models -Disk On/Busy, the indicator signals not only that the disk is being accessed, but also that there is a disk in the drive);
Headphone jack with electronic or mechanical volume control.
To read information from the disk, a semiconductor laser is used, emitting in the infrared range - the wavelength is about 780 nm. The laser beam, passing through the focusing lens, falls on the reflective layer. The reflected beam is recorded by a photodetector. Based on the recorded signal, the passage of the optical head over the pits and gaps of the disk is determined, and the quality of focusing of the laser beam spot on the surface of the disk and its orientation along the center of the track is also checked.
The output of the photodetector produces a digital bit stream, which is decoded by removing additional zero bits. The result is a bitstream that is the original CIRC-encoded data stream with subcodes added. Therefore, the subcode channels are separated and CIRC decoding is performed next. At the CIRC decoding stage, most errors caused by stamping defects, inhomogeneity of disk materials, scratches on its surface, unclear definition of the lite/gap in the photodetector, etc. are detected and corrected. The resulting stream of bits represents useful information stored on disk.
DVD technology
Development of computers and computing systems made it possible to begin the active use of powerful compression algorithms, making it possible to fit on one disc not an hour and a quarter, but from 5 to 10 hours of music with virtually no loss of quality. However, for the video industry, the size of one disk was too small even with compression, and computer applications had already outgrown the capabilities of CD drives. DVD technology was designed to solve all these problems.
In accordance with this, a single standard was adopted, called DVD, or Digital Video Disc (later adopted as Digital Versatile Disc - digital multi-purpose disc). Then the first version of the specification for DVD-ROM and DVD-Video was published and a scheme for protecting digital copies from unauthorized duplication was adopted.
Currently there are standards for DVD-Video, DVD-ROM, DVD-Audio. Sound on DVD is supported by Mono, PCM Stereo, Dolby Surround (Prologic), Dolby Digital AC-3, THX, DTS standards. Sound standards Dolbv Digital AC-3, THX, DTS define six-channel sound, i.e. sound accompaniment according to the scheme: front speakers, center, rear speakers and subbuffer. Typically, the abbreviation “5.1” is used to denote six-channel sound, which means the use of the main five sound sources and a separate low-frequency unit - a subbuffer. Dolby ProLogic and Doiby Digital AC-3 differ in that Dolby Digital AC-3 has six independently recorded audio tracks, while Dolby ProLogic only processes a stereo signal in a special way and is an imitation of six-channel sound.
Thus, the sound on DVD discs is recorded in the most various formats, they all reproduce several independent channels of spatially compressed sound, thereby creating a realistic picture of what is happening.
DVD video is digital video compressed using the MPEG-2 algorithm and recorded on a DVD disc. Format - 25 frames per second with a resolution of 720 x 576 pixels with a color depth of 24-bit (PAL) or 30 frames 720 x 480 x 24-bit (NTSC). In uncompressed form, this is a stream of 30 MB per second, and a two-hour film will occupy more than 100 gigabytes.
DVDs have capacities ranging from 4.7Gb to 17Gb depending on the type. In this case, it is not the recording density that changes, but the type of information placement. The discs are single-sided single-layer, single-sided double-layer, double-sided single-layer and double-sided double-layer. In addition, there are combination wheels, which have two layers on one side and one on the other.
The method of storing information on a DVD-ROM is almost the same as that of a CD-ROM: along the metal substrate, grooves are located in a spiral, making up the so-called tracks. These grooves carry information that is read by a laser beam, converting the grooves into ones and zeros. The reflective substrate itself is covered with a protective layer of plastic that protects the disc from damage.
The difference between a DVD and a CD is the density of the recorded information. For example, a single-sided, single-level DVD disc stores approximately 4.7 GB of information (DVD-5 technology), while a regular CD disc stores only 650 MB. A new semiconductor laser emitter has been developed that uses a shorter wavelength (650-635 nm) than the CD-ROM drive laser (780 nm). After this, the distance between the tracks became smaller, and the grooves themselves on the disk (information storage devices) significantly decreased in size.
Following single-level disks, two-level disks appeared, holding up to 8.54 GB of information. Here the first level was located under the second, and reading occurred by focusing the laser beam along the levels (DVD-9 technology). Using DVD-10 technology, reading occurs on both sides at the same level. The stored volume reached 9.4 GB. The dual-level DVD-18 provides 17.08 GB of storage. Reading occurs from two sides, each of which has two levels.
Important drive characteristics include Access Time, CPU Utilization central processor), Transfer Rate Inside/Outside (internal and external data transfer rates).
The Access Time indicator reflects the sum of the average search time required for a DVD-ROM drive to position itself on the desired track and the average “lag” time (latency) during which the disk is brought to the desired sector for reading. Accordingly, the lower the Access Time value, the better. The CPU Utilization indicator tells you how much the DVD-ROM uses processor resources.
Data transfer speed is characterized by two indicators: internal (Inside) and external (outside) speed. The internal bit rate is the transfer between the DVD disc and the DVD-ROM's internal buffer directly.
It is determined by many parameters: recording quality and density, rotation speed, etc. These parameters are influenced by the design feature of the drive. The external data transfer rate depends entirely on the transmission mode used.
Despite the wide variety of hard drive models, their operating principles and basic structural elements are the same. Figure 5 shows the main design elements of a hard disk drive:
· magnetic disks;
· read/write heads;
· head drive mechanism;
· disk drive motor;
· printed circuit board with electronic control circuit.
A typical drive consists of a sealed housing (hermoblock) and an electronic unit board. The HDA contains all the mechanical parts, and the board contains all the control electronics. A spindle with one or more magnetic disks is installed inside the HDA. The engine is located underneath them. Closer to the connectors, on the left or right side from the spindle there is a rotary positioner magnetic heads. The positioner is connected to the printed circuit board by a flexible ribbon cable (sometimes solid wires).
The hermetic block is filled with air under pressure of one atmosphere. In the covers of the hermetic blocks of some hard drives there is a special hole, sealed with a filter film, which serves to equalize the pressure inside and outside the block, as well as to absorb dust.
Figure 5 - Main design elements of the drive on hard drives
dimensions hard drives are standardized according to a parameter called form factor (Form-Factor). For example, all HDDs with a 3.5" form factor have standard sizes housing 41.6x101x146 mm.
Magnetic disk substrates The first hard drives were made of aluminum alloy with the addition of magnesium. Modern models use a composite material of glass and ceramics with a low thermal expansion coefficient as the main material for disk plates, which makes them less susceptible to temperature changes and more durable. Magnetic disks are available in the following sizes: 3.5"; 5.25"; 2.5"; 1.8".
The discs are covered with a magnetic substance - the working layer. It can be either oxide or thin film based.
Read/write heads provided for each side of the disc. When the drive is turned off, the heads touch the disk. When the disks unwind, the aerodynamic air pressure on the heads increases, which leads to their separation from the working surfaces of the disks. The closer the head is to the disk surface, the higher the amplitude of the reproduced signal.
Head drive mechanism ensures the movement of the heads from the center of the disks to the edges and actually determines the reliability of the drive, its temperature stability and vibration resistance. All existing head drive mechanisms are divided into two main types: with stepper motor and a moving coil.
Drive motor causes the disk pack to rotate, the speed of which, depending on the model, is in the range of 3600 - 7200 rpm (i.e. the heads move at a relative speed of 60 - 80 km/h). The rotation speed of some hard drives reaches 15,000 rpm. HDD rotates continuously even when it is not accessed, so the hard drive should only be installed vertically or horizontally.
Printed circuit board with electronic circuit controls and other drive components (front panel, configuration elements and mounting parts) are removable. Electronic circuits for controlling the motor and head drive and a circuit for exchanging data with the controller are mounted on the printed circuit board. Sometimes the controller is installed directly on this board.
Questions for self-control:
1. Floppy drives. Design, operating principle, main components, specifications FDD;
2. Logical structure of floppy disks;
3. Hard disk drives. Design and operating principle of HDD, form factors, types;
4. Main characteristics and operating modes of hard disk drives. Controllers and HDD connection;
5. Modern storage models;
6. Logical structure hard drive;
7. Formatting hard drives;
8. Utilities maintenance of hard magnetic disks.
Topic 4.2 CD-R (RW) drives. DVD-R (RW)
The student must:
have an idea:
· about the purpose of CD-R (RW) drives. DVD-R (RW)
know:
· operating principle and main components of a CD-ROM drive;
· CD-ROM drive performance characteristics;
· operating principle and main components of a DVD drive;
be able to:
· connect CD and DVD drives;
CD-R, (RW), DVD-R (RW) drives: operating principle, design and main components, technical characteristics.
Guidelines
CD-ROM drives
CD-ROM - compact disc (CD) intended for storage in digital form pre-recorded information on it and reading it using a special device called a CD-ROM driver - a drive for reading CDs.
The CD manufacturing process includes several stages.
At the first stage, an information file is created for subsequent recording on the medium. At the second stage, using a laser beam, information is recorded onto a medium, which is a fiberglass disk coated with a photoresist material. Information is recorded in the form of a sequence of spirally arranged indentations (strokes), as shown in Figure 6. The depth of each pit stroke (pit) is 0.12 µm, the width (in the direction perpendicular to the plane of the drawing) is 0.8 - 3.0 µm. They are arranged along a helical track with a spacing of 1.6 µm between adjacent turns, corresponding to a density of 16,000 TPI (625 TPI). The length of the streaks along the recording track ranges from 0.83 to 3.1 µm.
Figure 6 - Geometric characteristics of a compact disc (a) and its cross section (b)
At the next stage, the photoresist layer is developed and the disk is metallized. A disc made using this technology is called a master disc. To replicate CDs, several working copies are made from the master disc using electroplating. Working copies are coated with a more durable metal layer (for example, nickel) than the master disk, and can be used as matrices for duplicating CDs up to 10 thousand pieces. from each matrix. Replication is carried out by hot stamping, after which the information side of the disc base, made of polycarbonate, is vacuum metallized with a layer of aluminum and the disc is coated with a layer of varnish. Disks made by hot stamping, in accordance with the passport data, provide up to 10,000 cycles of error-free data reading. The thickness of the CD is 1.2 mm, diameter - 120 mm.
The CD-ROM drive contains the following main functional units:
· boot device;
· optical-mechanical unit;
· drive control and automatic control systems;
· universal decoder and interface unit.
Figure 7 shows the design of the optical-mechanical unit of the CD-ROM drive, which works as follows. An electromechanical drive rotates a disk placed in the loading device. The optical-mechanical unit ensures that the optical-mechanical reading head moves along the disk radius and reads information. A semiconductor laser generates a low-power infrared beam (typical wavelength 780 nm, radiation power 0.2 - 5.0 mW), which hits a separation prism, is reflected from a mirror and focused by a lens on the surface of the disk. The servo motor, following commands from the built-in microprocessor, moves a movable carriage with a reflective mirror to the desired track on the CD. The beam reflected from the disk is focused by a lens located under the disk, reflected from the mirror and hits a separation prism, which directs the beam to a second focusing lens. Next, the beam hits a photosensor, which converts light energy into electrical impulses. Signals from the photosensor are sent to a universal decoder.
Figure 9 - Design of the optical-mechanical CD-ROM drive unit
Automatic tracking systems for the disk surface and data recording tracks ensure high accuracy of information reading. The signal from the photosensor in the form of a sequence of pulses enters the amplifier of the automatic control system, where tracking error signals are isolated. These signals enter automatic control systems: focus, radial feed, laser radiation power, linear speed of disk rotation.
A universal decoder is a processor for processing signals read from a CD. It consists of two decoders, a random access memory device and a decoder control controller. The use of double decoding makes it possible to recover lost information up to 500 bytes. The random access memory serves as a buffer memory, and the controller controls the error correction modes.
The interface unit consists of a digital-to-analog converter, a low-pass filter and an interface for communication with a computer. When playing audio information, the DAC converts the encoded information into an analog signal, which is fed to an amplifier with an active filter low frequencies and then to the sound card, which is connected to headphones or speakers.
The following are performance characteristics that must be taken into account when choosing a CD-ROM in relation to specific tasks.
Data Transfer Rate (DTK) - The maximum speed at which data is transferred from the storage medium to RAM computer. The high data transfer speed of a CD-ROM drive is necessary primarily for synchronizing picture and sound. If the transmission speed is insufficient, video frames may be dropped and audio may be distorted.
Reading quality is characterized by the error rate (Eror Rate) and represents the probability of receiving a distorted information bit when reading it.
Average Access Time (AT) is the time (in milliseconds) it takes the drive to find the data it needs on the media.
Buffer capacity is the amount of random access memory in a CD-ROM drive used to increase the speed of access to data recorded on the media. Buffer memory(cache memory) is a memory chip installed on the drive board for storing read data.
Mean time between failures is the average time in hours that characterizes the failure-free operation of a CD-ROM drive.
In the process of developing storage devices on optical disks A number of basic formats for recording information on CD have been developed.
CD-DA (Digital Audio) format - digital audio compact disc with a playing time of 74 minutes.
The ISO 9660 format is the most common standard for the logical organization of data.
The High Sierra (HSG) format was proposed in 1995. and allows data written to disk in ISO 9660 format to be read by all types of drives, which has led to widespread replication of programs on CD and contributed to the creation of CDs targeting various operating systems.
The Photo-CD format was developed in 1990-1992. and is intended for recording on CD, storing and playing static video information in the form of high-quality photographic images. A Photo-CD format disc holds from 100 to 800 photographic images of the corresponding resolutions - 2048 x 3072 and 256 x 384, and also stores audio information.
Any CD-ROM disc containing text and graphic data, audio or video information is classified as multimedia. Multimedia CDs come in a variety of formats for different operating systems: DOS, Windows, OS/2, UNIX, Macintosh.
The CD-I (Jntractive) format was developed for a wide range of users as a standard multimedia disc containing various text, graphic, audio and video information. A CD-I format disc allows you to store a video image with sound (stereo) and a playback duration of up to 20 minutes.
The CD-DV (Digital Video) format provides recording and storage of high-quality video with stereo sound for 74 minutes. During storage, compression is provided using the MPEG-1 (Motion Picture Expert Group) method.
Reading the disc is possible using a hardware or software MPEG decoder.
The 3DO format was developed for game consoles.
CD-ROM drives can operate with either a standard IDE (E-IDE) interface or a high-speed SCSI interface.
The most popular CD-ROM drives in Russia are products with trademarks Panasonic, Craetive, Samsung, Pioneer, Hitachi, Teac, LG.
DVD drives
Solving the problem of increasing the capacity of optical storage media based on improving the production technology of CDs and drives, as well as existing scientific and technical solutions in the field of high-quality digital video, led to the creation of CDs with increased capacity.
The image quality stored in DVD format is comparable to the quality of professional studio video recordings, and the sound quality is also not inferior to studio quality. Audio information in DVD format is read at a speed of 384 KB/s, which makes it possible to organize multi-channel audio.
Such disk capabilities DVD format due to improved parameters of the working surface of the disks. Like CDs, DVDs have a diameter of 120 mm. IN DVD drive A semiconductor laser with a radiation wavelength in the visible region of 0.63 - 0.65 microns is used. This reduction in wavelength (compared to 0.78 microns for a conventional CD drive) made it possible to reduce the size of recording lines (pits) by almost half, and the distance between recording tracks - from 1.6 to 0.74 microns. The pits are arranged in a spiral, like on vinyl long-playing records.
DVD-ROM drives come with both a hardware MPEG-2 decoder in the form of an expansion card for the PCI bus, and a software decoder. DVD-R Writers and Rewriters DVD-RW drives capable of working with single-layer, single-sided disks with a capacity of up to 4.7 - 5.2 GB with an information writing speed of about 1 MB/s.
Questions for self-control:
1. CD-R, (RW) drives, operating principle, design and main components, technical characteristics;
2. DVD-R (RW): operating principle, design and main components, technical characteristics.
Principles of recording information on a DVD disc
The methods used to burn information to a DVD are similar to those used to burn a traditional CD. Currently, playback-only CDs, write-once CD-Rs, and rewritable CD-RWs are produced.
Principles of recording information on CDs, CD-ROMs, DVD-ROMs.
As shown in Figure 1 - a conventional compact disc (CD) consists of a transparent polymer substrate ( 1
), metallized reflective layer ( 2
) with "holes" ( B), with the help of which digital information is recorded, and a protective layer ( 3
), necessary to impart rigidity to the disk. Reflective layer ( 2
) in a regular CD and is a layer that stores information. It is manufactured using a factory method and is a kind of matrix with “holes” “stamped” in certain places, which indicate a logical unit. The absence of a "hole" implies a logical zero.
Information is read using a laser beam reflected from
disk surface. When reflected from the “hole”, the laser beam accurately hits a special detector, which outputs “1”. When reflected from a surface, the beam passes by the detector, which in this case recognizes "0". Absolutely the same principles of recording information underlie first-generation DVDs; they are intended only for reading information recorded on them in a factory way (the so-called DVD-ROM), CD-R, DVD-R.
In the compact disc record-once (CD-R) design, between the substrate ( 1
) and reflective layer ( 2
) there is a pigment layer ( 4
) from metal-stabilized cyanide (organic substance). In this case, it is the pigment layer on which the tracks are factory “extruded” ( A), along which the laser beam moves, stores information. When recording such a disc in special recorders, a high-power laser beam “burns” “holes” in the required places in the pigment layer ( B). When reading information, a laser beam of normal power freely passes through a “hole” in the pigment layer ( 4
), reflected from the metallized layer ( 2
) and hits the detector, which recognizes a logical one. In the absence of a “hole,” the laser beam is absorbed by the pigment layer, the laser beam is not reflected, and the detector outputs a logical zero. It should be noted that there is an additional rough layer for overprinting (5), on which the user, after recording information, can draw his own label using a ballpoint pen, a felt-tip pen, or even a special inkjet printer.
CD-RW, DVD-RAM.
The principle of recording on rewritable DVDs (which was originally developed for compact discs with the working title CD-Erasable) was proposed by Philips, Ricoh and Hewlett-Packard and supported by such companies as IBM, Sony, 3M, Olympus, Matsushita and Mitsumi. The compact disc rewritable (CD-RW) design is similar to a CD, but instead of a reflective layer, it uses a special substance ( 6
), capable of repeatedly changing its structure. This material was developed by TDK and called AVIST; it has almost ideal characteristics.
Its high reflectivity (25-35%) is sufficient for DVD compatibility during playback. The characteristics of AVIST material are stable at both high and low recording speeds, which is especially important when working with various applications. In the case of rewritable CDs (eg CD-Erasable), recording takes place at speeds below 3 m/s. Working with data in the rewritable DVD-RAM format requires the working layer to have a write speed of 3 to 6 m/s. When working with compressed video information, the recording speed should already be above 6 m/s.
Excellent signal-to-noise ratio and phase change characteristics allowed TDK to achieve ultra-small marker sizes (less than 0.66 mm).
New material AVIST can withstand at least 1000 rewrite cycles at speeds below 3 m/s. With more high speeds recording, this number of rewrite cycles should increase.
Just like on the pigment layer of a recordable disc, tracks are “extruded” on the AVIST working layer ( A), directing the laser beam. When recording such a disc, the substance, under the influence of a powerful laser beam, changes its structure at the desired point on the surface, passing from a crystalline state to an amorphous one. Since such a transition is reversible (that is, the substance can be transferred back to the crystalline state), the disk can theoretically be rewritten an almost infinite number of times. It all depends on the properties of the material used in the information layer ( 6
), and as it is further improved, the actually achievable number of cycles will increase and amount to at least five million rewrites. Reading is performed with a laser beam of normal power. When reflected from the surface of the disk, the phase of the laser beam changes depending on whether the reflection occurred from a surface area with an amorphous or crystalline structure. Changes in the phase of the reflected beam are recognized by the detector, which converts them into a digital stream. This method is called Phase Change Technology.
Single layer DVDs. As we have already noted, DVD is in many ways similar to CD, but differs significantly from it in recording density. As is clear from the recording principles described above, it is the maximum number of “holes” that can be placed on the surface of a disk that determines its information capacity.
The first step towards creating a new standard can be considered a sevenfold increase in the capacity of a CD due to an increase in recording density, which became possible thanks to the use of more advanced laser beam sources. differences in the size and density of the “holes”
Figure 2 shows the differences in the size and density of the “holes” in the working layer between DVD and CD discs.
Conventional CD-ROM drives use a 780 nm laser source that emits invisible infrared light. DVD players and DVD-ROMs use a laser emitting red light with a wavelength of 650 (635) nm. This reduction in wavelength made it possible to read smaller “holes” in the working layer of the disk, located in more densely spaced tracks (recording tracks). A corresponding increase in the numerical aperture of the lens (Numerical Aperture - the angle between the outer rays of the light cone entering the optical device) from 0.45 to 0.60 makes it possible to focus the laser beam with much greater accuracy. Only by increasing the recording density was it possible to increase the disk capacity to 4.7 GB.
In addition, digital modulation and error correction schemes have undergone significant modernization. State-of-the-art, high-efficiency modulation scheme (EFM Plus) operates in both 8- and 16-bit modes, ensuring compatibility with existing CD formats while allowing for more High Quality when using new DVD media. New scheme error correction (RS-PC Reed Solomon Product Code) is approximately 10 times more effective than that used in modern reading systems. single-sided single-layer disc (top) and single-sided double-layer disc (bottom)
Double layer DVDs. A further increase in disc capacity has been achieved through the development of a dual-layer DVD disc (DVD-9 standard). As can be seen from Fig. 3, a double-layer disk (lower diagram) has two whole working layers for recording information. To implement this model, a special translucent material was created for the outer information layer. When reading information from such a disk, the laser beam first passes through this translucent layer, focusing exclusively on the tracks of the inner layer (the principles of reading are described above). Having read all the information from the first (inner) layer, the laser beam automatically changes its focus, thereby changing the “penetration depth”, and begins reading information from the second (outer translucent) layer. The presence of two working layers allows you to increase the capacity to 8.5 GB. Since focus switching is almost instantaneous, and the use of an electronic buffer ensures that there are no interruptions in the outgoing digital stream, the dual-layer DVD model is intended to be used in applications that require large and “continuous” capacity.
The first layer of a two-layer DVD is stamped from ordinary polycarbonate-based plastics and carries the recording on one side. This side is then filled with a thin layer of translucent material, which in turn is covered with a film of photopolymer material, forming the outer working layer. The photopolymer material is hardened by ultraviolet irradiation, and the DVD is filled with transparent plastic, which serves as a protective layer for the disc. The main difficulty lies in creating a translucent material that separates the recording layers, since the requirements for it are quite contradictory: it must reflect the laser beam well (the required reflectance is about 40%) in the process of reading the outer layer and at the same time be as transparent as possible when reading the inner one layer. Priority in the development of such material belongs to 3M, which worked on behalf of Philips-Sony.
Double sided DVDs.
The total thickness of all layers of a DVD disc (both single-layer and double-layer) is only 0.6 mm, which is half the thickness of a CD disc. To be physically compatible with traditional CDs, the thickness of the DVD must be equal to the thickness of the CD, i.e. 1.2 mm. In a single-sided single-layer disc (DVD-5 standard), an additional 0.6 mm thick substrate is glued to the back side (the one where the CD label is located).
But this thickness makes it possible to produce a double-sided single-layer disc (DVD-10 standard). This idea was proposed by Toshiba. Structurally, the production process is as follows: two separate single-sided DVD discs are glued together with their back sides. As a result, the total thickness of the disc is the same as that of a standard CD - 1.2 mm, but such a disc can hold twice as much information; In addition, by reducing the thickness of the protective layer, the likelihood of information reading errors that occur in CDs due to random deviations of the laser beam in the transparent protective layer is reduced.
Thus, by combining (yes or no) two technologies for “doubling” the number of working surfaces, we obtain four structurally different DVD formats specified in the standard.
A single-layer, single-sided DVD-5 disc is primarily used for video films, as its capacity is sufficient for 92% of films, as well as for most computer applications, for which 4.7 GB of capacity is sufficient. At the same time, such a disc turns out to be a relatively cheap medium - its cost is only 14% higher than the cost of producing a traditional CD.
The next most complex disc type is single-sided, double-layer DVD-9. This type of disk is most widely used in applications where high capacity is a prerequisite without interruptions in reading.
Toshiba's DVD-10 (double-sided single-layer disc) format involves manually flipping the disc after playing one side; It is advisable to use it, for example, for duplicating very long films or TV series that do not fit on a single-layer, single-sided disc. Subsequently, with a further reduction in the total thickness of all working layers of the disc, it is possible to create a high-capacity double-sided double-layer DVD-17.
Technical characteristics with DVD disc specifications
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