CD-ROM

CD-ROM Drive (Dell)

Print vs. bytes

CD laser assembly1

Cd-rom-drive-reading-head-movement

Plextor PX-W8432Ti - laser-lens-unit-4539

Compact Disc Read-Only Memory (CD-ROM) is a type of optical disc that is used to store data. Unlike its audio counterpart, the Compact Disc (CD), which was primarily designed for audio playback, CD-ROMs are utilized for storing and accessing data by computers. The development and introduction of the CD-ROM in the mid-1980s marked a significant advancement in data storage and digital media, paving the way for the widespread distribution of software, games, encyclopedias, and multimedia content.

History

The CD-ROM was developed as an extension of the audio CD, which itself was introduced in 1982 as a collaboration between Sony and Philips. The standard for CD-ROMs was established in 1985, defined in the Yellow Book, which was an extension of the Red Book standard used for audio CDs. This standard outlined the physical and logical format for the data stored on a CD-ROM, including the filesystem standard (ISO 9660) that allows a CD-ROM to be read by computers with different operating systems.

Technology

A CD-ROM stores data in the form of tiny indentations (pits) and flat areas (lands), which are encoded in a spiral track on the disc. A laser beam reads the disc by reflecting off the surface, with changes in reflectivity corresponding to binary data (1s and 0s). CD-ROMs are read-only, meaning the data written to them during manufacturing cannot be modified or erased.

The standard size of a CD-ROM can hold up to 700 MB of data, which was a significant increase over the floppy disks used prior to the CD-ROM's introduction. The data transfer rate of a CD-ROM drive, which reads the discs, is measured in multiples of 150 kilobytes per second (KB/s), with speeds ranging from 1x to 72x.

Usage

CD-ROMs became an essential medium for software distribution, including operating systems, application software, and video games. They were also widely used for storing large databases, educational materials, and multimedia content, such as music and video, which benefitted from the CD-ROM's high capacity and durability compared to magnetic storage media.

Decline

With the advent of DVDs, which offer higher storage capacity, and later USB flash drives, cloud storage, and streaming media, the popularity and usage of CD-ROMs have significantly declined. However, they remain an important part of the history of digital storage and are still used in some contexts where a physical copy of data is required.

See Also

• Optical disc drive
• Floppy disk
• Hard disk drive
• Solid-state drive

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