What is SD ROM? CDs and CD-ROM drives. Operating principle of a CD-ROM drive
172.3 Kbps (audio from CD-DA)
CD-ROM drives are a popular and cheapest means for distributing software, computer games, multimedia and other data. CD-ROM (and later DVD-ROM) became the main medium for transferring information between computers, displacing the floppy disk from this role (it is now giving way to more promising solid-state media).
Often the term CD-ROM mistakenly used to refer to the drives (devices) themselves for reading these disks (correctly - CD-ROM Drive, CD drive).
Technical details
A compact disc is a 1.2 mm thick polycarbonate substrate, covered with a thin layer of metal (aluminium, gold, silver, etc.) and a protective layer of varnish, on which a graphic representation of the contents of the disc is usually applied. The principle of reading through the substrate was adopted because it makes it possible to very simply and effectively protect the information structure and remove it from the outer surface of the disk. The diameter of the beam on the outer surface of the disk is about 0.7 mm, which increases the system's immunity to dust and scratches. In addition, on the outer surface there is an annular protrusion 0.2 mm high, which allows the disk, placed on a flat surface, not to touch this surface. There is a hole with a diameter of 15 mm in the center of the disk. The weight of the disc without the box is approximately 15.7 g. The weight of the disc in a regular (not “slim”) box is approximately 74 g.
CDs are 12 cm in diameter and originally held up to 650 MB of information. However, starting around 2000, 700 MB disks began to become increasingly widespread, subsequently completely replacing the 650 MB disk. There are also media with a capacity of 800 megabytes or even more, but they may not be readable on some CD drives. There are also 8-centimeter disks that can hold about 140 or 210 MB of data and CDs shaped like credit cards (so-called business card disks).
CD-ROM under an electron microscope
Information on the disk is recorded in the form of a spiral track of so-called pits (recesses) extruded into a polycarbonate base. Each pit is approximately 100 nm deep and 500 nm wide. Pit length varies from 850 nm to 3.5 µm. The spaces between pits are called lands. The pitch of the tracks in the spiral is 1.6 microns.
There are read-only disks (“aluminum”), CD-R - write-once, CD-RW - write-multiple. The last two types of discs are designed for recording on special burner drives.
CD business card
CD business card is an optical disk made in the format of a business card (repeats its size 90×50 mm).
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See what "CD-ROM" is in other dictionaries:
Rom- (Roma) ... Deutsch Wikipedia
Rom: Großmacht und Weltreich- Rom hatte vor dem Pyrrhoskrieg jahrzehntelange höchst aufreibende Kriege geführt und brauchte Ruhe. Es beschäftigte sich damit, allerlei Nachbereinigungen vorzunehmen, um die Herrschaft Schritt für Schritt zu sichern, und errichtete in aller… … Universal-Lexikon
Rom- (Roma), die merkwürdigste Stadt auf der Erde, gegenwärtig die Hauptstadt des Kirchenstaats, liegt unterm 41°53 54 nördl. Breite, 10°9 30 östl. Länge zu beiden Seiten der Tiber, 3 etc. Ml. von deren Mündung auf den bekannten 7 Hügeln (mons… … Herders Conversations-Lexikon
ROM hacking- is the process of modifying a video game ROM image to alter the game s graphics, dialogue, levels, gameplay, or other gameplay elements. This is usually done by technically inclined video game fans to breathe new life into a cherished old game,… … Wikipedia
ROM- bezeichnet: Rom, die Hauptstadt Italiens Provinz Rom, die nach der Stadt Rom benannte italienische Provinz Römisches Reich, in der Zeit vom 6. Jahrhundert v. Chr. bis zum 6. Jahrhundert n. Chr. Zweites Rom, Konstantinopel, antique Hauptstadt des… … Deutsch Wikipedia
Rom (Begriffsklärung)- Rom bezeichnet: Römisches Reich, in der Zeit vom 6. Jahrhundert v. Chr. bis zum 6. Jahrhundert n. Chr. Römische Kurie, die Zentralbehörde des Heiligen Stuhls für die römisch katholische Kirche einen männlichen Angehörigen der Roma… … Deutsch Wikipedia
CD-ROM/XA (extended Architecture) by its name suggests that this is a CD-ROM disk with extended capabilities. The disc supports ISO 9660 and High Sierra file systems. Let's take a closer look at what these opportunities are.
Multiple recording. The High Sierra format on a regular CD-ROM allows only one table of contents to be written when creating an entry. Due to this, additional recording of the disc is impossible. XA discs have the ability to record a disc in multiple sessions because they can work with multiple tables of contents.
Alternation. CD-ROM/XA operates in Mode 2. Let us repeat that in this mode, each sector of the track can have its own format. Form 1 of this mode is used to store data, and Form 2 is used for video, music and images. This mode was conceived specifically for recording multimedia applications, so that on one track you could alternate, for example, program code and sound (video) for it. At the beginning of each fragment a special “flag” is placed, by which its type is determined. XA discs are very convenient to use for video recording, because you can first record a video frame and immediately follow it with audio. Naturally, their synchronization is already performed programmatically. As an example, four possible music encoding schemes are shown below (A-audio data encoded using the ADPCM method, D-data).
Music data compression. XA mode allows you to record several hours of music on a regular 74-minute disc. This becomes a possible compression method. To increase the volume of audio data, non-16-bit PCM encoding is used in this case (pulse code modulation is used to digitize analog signals before transmitting them. Almost all types of analog data, such as video, voice, music, telemetry data, virtual worlds allow its use), and 4 or 8-bit ADPSM coding (differential (or delta) pulse code modulation.
A speech encoding method that involves calculating the difference between two successive values of a signal digitized using the PCM method). The sampling frequency may also change. Depending on the sound quality, CD-ROM/XA offers two levels of audio encoding: Level B (sampling rate 37.8 kHz mono or stereo) and Level C (sampling rate 18.9 kHz mono or stereo). Depending on the situation, one or another level is applied. DVD replication. For example, these voices do not require high sound quality. Therefore, by encoding your voice at Level C, you can get a huge increase in available disk space. Although music at this level will be unpleasant to listen to.
This is a device for reading data that is recorded on an optical CD.
The storage medium on the CD is relief polycarbonate substrate 120, 80 mm, on which a thin layer of light-reflecting metal (aluminum, sometimes gold) is applied. When recording a CD matrix, a laser beam “burns” tiny holes in it - pits, leaving reflective surfaces of the metal disk - lands. After this, the matrix (master disk) is sent to the production workshop, where many polycarbonate copies are stamped from it. Then the relief base is metallized, and another, thinner layer of varnish is added to protect the metal layer.
When reading a disc, a different reading beam is reflected from the pits and lands in different ways. More precisely, it is not reflected from the pits - the pits absorb the beam and do not allow it to be reflected. Thus, the pit gives a “zero” signal, and the land gives a “one”. And the combination of zeros and ones is the essence of any computer information. From the center to the edge of the CD, one track 0.4 µm wide is applied in a spiral with a pitch of 1.6 µm.
The entire surface of the CD is divided into three sections in the form of rings, located from the center to its edge. The Lead-In area is located closer to the center of the disk. When a disk is initialized in a personal computer, the Lead-In area is read first. This area contains the disk title, Table of Contents, a table of addresses of all records, the disk label and some service information. The middle area contains the main information on the CD and occupies the bulk of the disc. The Lead-Out disc area contains the end of disc mark.
What does a CD-ROM consist of?
The CD-ROM drive consists of the main components:
- an electric motor that rotates the disk;
- an optical system, which consists of a laser emitter, optical lenses and sensors, designed to read information from the surface of a compact disc,
- microprocessors that control the mechanics of the drive, the optical system and decoding the read information into binary code.
The CD is spun by an electric motor. The beam from the laser emitter is positioned in the desired area using an optical drive system. The beam is reflected from the surface of the disk and passes through a prism to a special sensor. The stream of rays is converted by the sensor into an electrical signal, which is processed.
CD-ROM capacity. The capacity of CD-ROM is 650-700 MB (on disks with a diameter of 80 mm - 180-210 MB). This type of disc can hold 74 minutes of audio or up to 2 hours of television-quality video in MPEG-4 format.
CD-ROM transfer speed. Data Transfer Rate is a value that characterizes the maximum speed at which the drive transfers data read from a CD to RAM. The data transfer rate increases from the initial sectors to the final ones. The transfer speed of the inner disk ring is called the Inside Data Transfer Rate, and the outer ring is called the Outside Data Transfer Rate. The technical data sheet provides the external speed. Thus, the Sony 52x drive is a 52-speed drive from Sony. Data is read 52 times faster than disk drives (or a conventional audio player), whose read speed is 150 kB/s. That is, multiplying 52 by 150, we get the data transfer speed of the Sony 52x drive equal to 7800 kB/s.
Optical drives
Since 1995, the basic configuration of a personal computer began to include a CD-ROM drive instead of 5.25-inch drives. The abbreviation CD-ROM (Compact Disk Read Only Memory) is translated as a read-only storage device based on compact discs. The operating principle of this device is to read digital data using a laser beam that is reflected from the surface of the disk. A regular CD is used as a storage medium. Digital recording on a CD differs from recording on magnetic disks in its high density, so a standard CD has a capacity of about 650-700 MB. Such large volumes are typical for multimedia information (graphics, music, video), so CD-ROM drives are classified as multimedia hardware. In addition to multimedia publications (electronic books, encyclopedias, music albums, videos, computer games), a variety of large-scale system and application software (operating systems, office packages, programming systems, etc.) are distributed on CDs.
CDs are made of transparent plastic with a diameter of 120 mm. and thickness 1.2 mm. A layer of aluminum or gold is sprayed onto the plastic surface. In mass production conditions, information is recorded on a disk by extruding tracks on the surface in the form of a series of indentations. This approach provides binary recording of information. Recess (pit - pit), surface (land - land). Logical zero can be represented by either a pit or a land. A logical one is encoded by the transition between pit and land. From the center to the edge of the CD there is a single track in the form of a spiral 4 microns wide with a pitch of 1.4 microns. The surface of the disk is divided into three areas. Lead-In is located in the center of the disk and is read first. It records the contents of the disk, a table of addresses of all records, the disk label and other service information. The middle area contains basic information and takes up most of the disk. The Lead-Out area contains the end-of-disk mark.
For stamping, there is a special prototype matrix (master disk) of the future disk, which extrudes tracks on the surface. After stamping, a protective film of transparent varnish is applied to the surface of the disc.
The CD-ROM drive contains:
- an electric motor that rotates the disk;
- an optical system consisting of a laser emitter, optical lenses and sensors and designed to read information from the surface of the disk;
- a microprocessor that controls the drive mechanics, the optical system and decodes the read information into binary code.
The CD is spun by an electric motor. A beam from a laser emitter is focused onto the surface of the disk using an optical system drive. The beam is reflected from the surface of the disk and fed through a prism to the sensor. The light flux is converted into an electrical signal, which enters the microprocessor, where it is analyzed and converted into binary code.
Main characteristics of CD-ROM:
- data transfer rate - measured in multiples of the speed of an audio CD player (150 KB/sec) and characterizes the maximum speed at which the drive transfers data to the computer's RAM, for example, a 2-speed CD-ROM (2x CD-ROM) will read data speed 300 KB/sec, 50-speed (50x) - 7500 KB/sec;
- access time - the time required to search for information on a disk, measured in milliseconds.
The main disadvantage of standard CD-ROMs is the inability to write data, but there are CD-R write-once and CD-RW write-once devices.
CD-R (CD-Recordable) drive
Externally similar to CD-ROM drives and compatible with them in disc size and recording formats. Allows one-time recording and an unlimited number of readings. Data recording is carried out using special software. The recording speed of modern CD-R drives is 4x-8x.
CD-RW (CD-ReWritable) drive
They are used for reusable recording of data, and you can either simply add new information to free space or completely overwrite the disk with new information (the previous data is destroyed). As with CD-R drives, to record data you need to install special programs on the system, and the recording format is compatible with a regular CD-ROM. The recording speed of modern CD-RW drives is 2x-4x.
DVD drive (Digital Video Disk)
A device for reading digital video recordings. Externally, a DVD disc is similar to a regular CD-ROM (diameter - 120 mm, thickness 1.2 mm), but differs from it in that up to 4.7 GB can be recorded on one side of the DVD disc, and up to 9.4 GB. If a two-layer recording scheme is used, up to 8.5 GB of information can be placed on one side, respectively, on two sides - about 17 GB. DVDs can be rewritten.
The most important factor hindering the widespread use of CD-R, CD-RW and DVD drives is the high cost of both them and removable media.
In the period 1994-1995, the basic configuration of personal computers no longer included floppy drives with a diameter of 5.25 inches, but instead the installation of a floppy drive became standard CD-ROM having the same external dimensions.
Abbreviation CD-ROM (Compact Disc Read-Only Memory) translated into Russian as CD-ROM-based read-only storage device . The operating principle of this device is to read numerical data using a laser beam reflected from the surface of the disk. Digital recording on a CD differs from recording on magnetic disks in its very high density, and a standard CD can store approximately 650 MB of data.
Large volumes of data are typical for multimedia information(graphics, music, video), so disk drives CD-ROM classified as multimedia hardware.
Today, multimedia publications are gaining an increasingly stronger place among other traditional types of publications. For example, there are books, albums, encyclopedias and even periodicals (electronic magazines) published on CD-ROM.
The main disadvantage of standard disk drives CD-ROM is the impossibility of recording data, but in parallel with them there are also write-once devices CD-R (Compact Disk Recorder) and rewritable devices CD-RW .
The main parameter of disk drives CD-ROM is the data reading speed. It is measured in multiples. The reading speed in the first production samples was taken as the unit of measurement, which was 150 KB/s. Thus, a drive with double the read speed provides performance of 300 KB/s, with quadruple speed - 600 KB/s, etc. Currently, the most common devices are CD-ROM reading with a productivity of 48x-52x. Modern examples of write-once devices have a performance of 16x-32x, and write-multiple devices - up to 32x.
By 1995, Philips and Sony developed a high-capacity compact disc, Multimedia CD. Toshiba and several other companies have created a different CD technology and also with increased capacity. The battle for the market has begun. Then the two largest groups, CITWG (Computer Industry Technical Working Group) and HVDAG (Hollywood Video Disc Advisory Group), came together to fight against the emergence of these incompatible standards. In 1995, through joint efforts, a new standard was created - DVD. It was intended primarily for the film industry, as a substitute for video cassettes, and therefore the abbreviation stood for Digital Video Disc. Then this format was renamed Digital Versatile Disc - digital versatile disk. However, in 1997, Philips and Sony left the consortium. Subsequently, other DVD manufacturers followed suit.
At the moment there are several DVD formats and this brings some confusion to the market because not all formats are compatible. There are DVD-R, DVD-ROM, DVD-RAM, DVD-RW. DVD-ROM drives without special modification cannot read DVD-RAM discs (with the exception of DVD-ROMs of the so-called third generation, produced since mid-1999). But DVD–RAM drives can read DVD–ROM, as well as CD–R and CD–RW. The DVD+RW drive is only compatible with DVD-ROMs and regular CDs. And the DVD + RW format is not recognized by many manufacturers at all. First-generation DVD-ROM devices used CLV mode and read from the disc at a speed of 1.38 MB/s (in traditional DVD notation this is 1x). Second-generation devices could read DVDs at twice the speed - 2x (2.8 MB/s). Modern DVD-ROMs - third-generation devices - use rotation control mode (CAV) with a maximum reading speed of 4x-6x (5.5 - 8.3 MB/s) or more.
The main differences between the DVD standard and CD:
1) a laser with a shorter wavelength is used. If in CD-ROM drives the wavelength is 780 nanometers, then in DVD drives it is 635 nanometers. This allows you to reduce the stroke length and increase the speed of data reading.
2) due to the use of more advanced materials, DVD is used to record data in two layers on one side of the disc or one layer on both sides of the disc or two layers on both sides of the disc, depending on the DVD format. Disk capacity varies from 2.6 Gb to 17 Gb.
3) a completely new sector format, a more reliable error correction code, and improved channel modulation are used. Now let's talk about layers in more detail.
Single Side/Single Layer
This is the simplest structure of a DVD disc. This disk can accommodate up to 4.7 GB of data. This capacity is 7 times greater than the capacity of a conventional audio CD and CD-ROM disc.
Single Side/Dual Layer
This type of disk has two layers of data, one of which is translucent. Both layers are read from one side and such a disk can accommodate 8.5 GB of data, i.e. 3.5 GB more than a single-layer/single-sided disc.
Double Side/Single Layer
This disk holds 9.4 GB of data (4.7 GB on each side). The capacity of such a disc is twice that of a single-sided/single-layer DVD disc. However, because the data is on both sides, you will have to flip the disk over or use a device that can read the data on both sides of the disk on its own.
Double Side/Double Layer
The structure of this disk allows you to store up to 17 GB of data on it (8.5 GB on each side).
The thickness of a DV disc is 0.6mm, which is half the thickness of a standard CD disc. This makes it possible to connect two disks with opposite sides and get a double-sided disk equal in thickness to a regular CD. Another technology creates a second layer to house data, which allows you to increase the capacity of one side of the disk. The first layer is made translucent, so the laser beam can pass through it and be reflected from the second layer.
Among other things, DV discs have the ability to increase recording density. To achieve this, manufacturers take different paths:
1. a more advanced laser is used
2. reduce stroke length
3. reduce the distance between turns
4. increase the data area without changing the overall disk size
5. Increase ECC efficiency
6. apply more efficient modulation
Now about rewritable discs. These include the DVD – RAM format. These discs use a material developed by TDK engineers and it is called AVIST. The recording principle is almost the same as that of a CD. The most important advantages of DVD-RAM format discs are the ability to be rewritten up to 100,000 times and the presence of a recording error correction mechanism. DVD+RW discs can record streaming video or audio, as well as computer data. DVD+RW format discs can be rewritten about 1000 times, but the DVD+RW format is promoted only by its developers - Hewlett-Packard, Mitsubishi Chemical, Philips, Ricoh, Sony and Yamaha and is not supported by the DVD forum. DVD-RW is a rewritable format developed by Pioneer. DVD-RW format discs hold 4.7 GB per side, are available in single-sided and double-sided versions and can be used to store video, audio and other data. DVD-RW discs can be rewritten up to 1000 times. Unlike DVD+RW and DVD-RAM formats, DVD-RW discs can be read on first-generation DVD-ROM drives.
A major achievement in ensuring compatibility in DVD technology was the unified file system MicroUDF, adopted in 2000. The MicroUDF file system is a version of the UDF (Universal Disk Format) file system adapted for use in DVDs, which, in turn, is based on the international standard ISO-13346. This file system is gradually replacing the outdated ISO9660, which was created at one time for use in CDs. For the transition period (until computer devices and disks operating in the ISO9660 format go out of circulation), the UDF Bridge file system will be used, which is some combination of MicroUDF and ISO9660. Only MicroUDF can be used to burn Audio/Video DVD discs.
To protect against illegal copying, two specifications have been developed: DVD-R(A) and DVD-R(G). These two versions of the same specification use different laser wavelengths when recording information. Thus, discs can only be written on equipment that meets their specifications. Disc playback can be performed equally successfully on any equipment that supports the DVD-R format. DVD-R(A) (DVD-R for Authoring) is used in professional applications. In particular, support for a special format (Cutting Master Format) allows you to use these discs to record the original replica of information (pre-mastering) instead of the usual use of DLT tapes for these purposes.
DVD-R(G) (DVD-R for General) is intended for wider use. Disks of this format are protected from the possibility of bit-by-bit copying of information onto them from other disks. The format is supported in mass storage devices (for example, in robotic DVD libraries offered by Pioneer itself).
