CD-ROM ( eng. Compact Disc Read-Only Memory , read: "sit-rum") - a type of CD-ROM with recorded data read-only ( read-only memory - read-only memory ). CD-ROM is a modified version of CD-DA (a disk for storing audio recordings) that allows you to store other digital data on it (physically no different from the first, only the format of the recorded data has been changed). Later versions were developed with the ability to write once ( CD-R ) and re-write ( CD-RW ) information to disk. A further development of the CD-ROM was DVD-ROM .
| Media type | |
|---|---|
| Title | Compact disc read-only memory |
| Abbreviation | CD-ROM |
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| general information | |
| Development date | 1979 |
| Developers | Philips , Sony |
| Dimensions | 120 × 1.2 mm |
| Capacity | 650—879 Mb |
| Read speed (1 ×) | 150 Kb / s (data from CD-ROM Mode 1) 172.3 Kbps (audio from CD-DA ) |
| Fastest reading speed | 72 × (10.8 Mb / s ) |
| Life time | 10-50 years |
| Work with optical discs | |
|---|---|
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| Types of Optical Discs | |
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| Formats | |
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| Protection technology | |
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CD-ROM is a popular and cheapest way to distribute software , computer games , multimedia and other data. In the early 2000s, CD-ROM (and later DVD-ROM) became the main medium for transferring information between computers , displacing the floppy disk from this role. Since the mid-2000s, it has ceded this role to more promising solid state carriers .
The format of recording on a CD-ROM also provides for recording information on a single disc of mixed content - both computer data ( files , software , reading is available only on a computer) and audio recordings (played on a regular audio CD player ), videos, texts and pictures. Such discs, depending on the order of the data, are called advanced ( English Enhanced CD ) or Mixed-Mode CD .
Often the term CD-ROM is mistakenly used to refer to the drives (devices) themselves for reading these disks (correctly - CD-ROM Drive , CD-drive ).
Content
Technical Details
A compact disc is a 1.2 mm thick polycarbonate substrate coated with the thinnest metal layer ( aluminum , gold , silver , etc.) and a protective varnish layer, on which a graphical representation of the disc content is usually applied. The principle of reading through the substrate was adopted, because it allows a very simple and effective protection of the information structure and remove it from the outer surface of the disk. The beam diameter on the outer surface of the disk is about 0.7 mm, which increases the noise immunity of the system to dust and scratches. In addition, on the outer surface there is an annular protrusion of 0.2 mm high, which allows the disk, laid on a flat surface, not to touch this surface. In the center of the disc is a hole with a diameter of 15 mm. The weight of a disk without a box is approximately 15.7 g. The weight of a disk in a regular (not “slim”) box is approximately 74 g.
Compact discs have a diameter of 12 cm and initially accommodated up to 650 MB of information. However, starting from about 2000, discs with a capacity of 700 MB began to become more and more widespread, subsequently completely replacing a disk with a capacity of 650 MB. There are also 800 megabytes or more media, but they may not be readable on some CD drives. There are also 8-centimeter disks, which can hold about 140 or 210 MB of data and CD, in the form resembling credit cards (so-called business card disks).
Information on the disk is recorded in the form of a spiral track of the so-called pits (indentations) extruded in a polycarbonate base. Each pit is approximately 100 nm deep and 500 nm wide. The length of the pit varies from 850 nm to 3.5 microns . The intervals between the pits are called Lend. The pitch of the tracks in the spiral is 1.6 μm.
Distinguish between read-only discs (“aluminum”), CD-R - for single recording, CD-RW - for multiple recording. The discs of the last two types are designed for recording on special recording drives.
CD Business Card
CD-business card - an optical disk, executed in the format of a business card (repeats its size 90 × 50 mm).
Designed to store personal data that complement the contact information printed on the front side of the CD business card.
The business card disk is designed for playback in a computer drive, its playback is provided by the location in its lower part of the bulges fixing the disk in an 8-cm recess for mini-DVD and mini-CD . Unlike CD postcards, the disc is made of a denser material and has a smaller radius, so there is less possibility of its rupture in a computer drive.
For options based on CD-technology, a characteristic volume of 20 MB.
The reverse side of the disk allows the application of marks and images on it, although there is a hole in the center of the disk.
Standards
There are several standards for storing data on digital optical discs. Collectively, they are called Rainbow Books . They include the Red Book - the standard for audio discs, the White Book - the standard for storing video data, the Yellow Book - the standard for storing computer data, and the Green Book - the standard for storing multimedia information on a disk, combining the three previous standard (see: CD-i ).