Stands for "Read-Only Memory."
ROM is a common hardware component found in electronic devices that stores the basic instructions that the device needs to operate. Unlike RAM, which is volatile temporary memory that is erased when powered off, ROM is non-volatile memory, where data is written to the chip and stays there even when removed from power. ROM chips are found in all electronic devices that need software instructions to carry out a task, from computers and smartphones to cars, microwave ovens, and electronic children's toys.
The software instructions written to a ROM chip are called firmware. Computers use a special ROM chip that contains a type of firmware called the BIOS to handle the basic tasks required to boot up and get the other components started.
There are several different types of ROM chips that can be used, depending on the technological needs of the device the ROM is used in.
- Masked ROM is the earliest form of ROM, where the software instructions are physically encoded directly into the circuits when the chip is manufactured.
- Programmable ROM, or PROM, is a ROM chip that is blank when manufactured and can be permanently written to a single time.
- Erasable Programmable ROM, or EPROM, is a type of programmable ROM that can be erased by exposing the circuits to ultraviolet light and written to again.
- Electronically Erasable Programmable ROM, or EEPROM, can be erased electronically and rewritten. This type of ROM allows for easy firmware updates on devices that use it, without requiring any other equipment.
- Flash Memory is a type of EEPROM that can be rewritten quickly. It used to be significantly more expensive than other types of ROM, limiting its use, but is now much cheaper and is the most common type of ROM chip technology.