A CD-ROM (Compact Disc Read-Only Memory) is a type of compact disc that can only be read, not written to. It is a digital storage medium that can hold large amounts of data, including text, images and audio.
The data on a CD-ROM is encoded in a spiral track that begins at the center of the disc and extends to the edge. This track is read by a laser, which is reflected back to a sensor in the CD drive.
The original data format for CD-ROM was defined by Philips and Sony in the 1983 Yellow Book. Other standards are used in conjunction with it to define directory and file structures, including ISO 9660, HFS (Hierarchical File System, for Macintosh computers) and Hybrid HFS/ISO.
The format of the CD-ROM is the same as for audio CDs: a standard CD is 120 mm (4.75 inches) in diameter and 1.2 mm (0.05 inches) thick and is composed of a polycarbonate plastic substrate (underlayer -- this is the main body of the disc), one or more thin reflective metal (usually aluminum) layers and a lacquer coating.
It works by being inserted into a CD drive, the drive's laser beam scans the surface of the disc, reading the data stored in the spiral track. The data is then converted into a digital signal that the computer can understand and process. The drive also has a lens that focuses the laser beam on the disc surface, allowing it to read the data accurately.
Constant Linear Velocity (CLV) is the principle by which data is read from a CD-ROM. This principle states that the read head must interact with the data track at a constant rate, whether it is accessing data from the inner or outermost portions of the disc. This is affected by varying the rotation speed of the disc, from 500 rpm at the center to 200 rpm at the outside.
Both CDs and CD-ROMs are types of optical discs that use a laser beam to read the data stored on them. However, while CDs are primarily used for audio content and can be written to, CD-ROMs are used for storing and distributing data such as software and can only be read.
There are several advantages to using CD-ROMs for software distribution. These include:
There are also some disadvantages to using CD-ROMs. These include:
In today's digital age, CD-ROMs might seem like a relic of the past. However, despite the rise of cloud storage and online downloads, CD-ROMs are still widely used for business software distribution.
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09 Feb 2023