CD-ROM (Compact Disc Read-Only Memory) is an optical disc format created by Sony and Philips and introduced in 1985 as the first extension of the Compact Disc format.
It is most commonly used to distribute software and video games, and is a read-only format (CD-R and CD-RW were introduced later as writeable formats). In the 1990s, the CD-ROM rapidly replaced the 3.5-inch floppy disk for software distribution. In recent years, the use of CD-ROM has declined as more software is distributed over the internet.
CD-ROM discs are physically identical to Compact Discs, only differing in the way data is stored on them, and like Compact Discs, can come in different sizes (such as 80mm Mini CD, and business card sizes). Full-size CD-ROM discs can store up to 737 MB of data. CD-ROM drive speeds are rated with a speed factor relative to audio CDs.
Early CD-ROM drives used a caddy that the disc had to be placed in before placing in the drive.
CD-ROM XA (eXtended Architecture) is a variation introduced in 1991 that allows for data, audio, and video to be accessed on the same disk.