CDROMs

CD-ROM stands for compact disc read-only memory, an optical disc storage medium designed for read-only access to digital data. Developed in the 1980s by Philips and Sony to accompany the audio CD, CD-ROMs were intended for software distribution, multimedia content, and data archival. A typical 120 mm disc stores about 650–700 MB of data, or roughly 74–80 minutes of audio, depending on the encoding and packaging.

Data on a CD-ROM are organized in sectors and read by a laser in a CD-ROM drive. The data capacity is described in multiples of 1x speed, with early drives starting at 1x and later models reaching higher speeds. Technically, a standard data CD uses 2,048 bytes per logical sector, with a raw sector of 2,352 bytes that includes error correction and synchronization. The data are encoded using modulation and protected by error correction codes such as CIRC (Cross-Interleaved Reed-Solomon Coding) to cope with physical imperfections on the disc.

File systems on CD-ROMs commonly employ ISO 9660, often with extensions such as Joliet or Rock Ridge to support longer filenames and Unix permissions. Because the medium is read-only, CD-ROMs are not writable without special hardware or formats; writeable variants such as CD-R and CD-RW were introduced later to allow user recording and revision.

Impact and legacy: CD-ROMs played a major role in software distribution, gaming, and multimedia in the late 1980s through the 1990s. They facilitated large-scale data sharing before the rise of DVDs, USB flash drives, and online distribution. Today, CD-ROMs are largely supplanted for new releases but remain in use for archival storage, compatibility-sensitive installations, and certain legacy applications.