A CD-ROM is a type of read-only memory consisting of a pre-pressed optical compact disc that contains data computers can read—but not write or erase—CD-ROMs. Some CDs, called enhanced CDs, hold both computer data and audio with the latter capable of being played on a CD player, while data is only usable on a computer.
A CD-ROM in the tray of a partially open CD-ROM drive.
A CD-ROM can easily store the entirety of a paper encyclopedia's words and images, plus audio & video clips.
A view of a CD-ROM drive's disassembled laser system
The laser system of a CD-ROM drive
Read-only memory (ROM) is a type of non-volatile memory used in computers and other electronic devices. Data stored in ROM cannot be electronically modified after the manufacture of the memory device. Read-only memory is useful for storing software that is rarely changed during the life of the system, also known as firmware. Software applications, such as video games, for programmable devices can be distributed as plug-in cartridges containing ROM.
Many game consoles use interchangeable ROM cartridges, allowing for one system to play multiple games. Shown here is the inside of a Pokémon Silver Game Boy cartridge. The ROM is the IC on the right labeled "MX23C1603-12A".
The first EPROM, an Intel 1702, with the die and wire bonds clearly visible through the erase window
Transformer matrix ROM (TROS), from the IBM System 360/20
An EPROM
