A+ Certification / Beginners

Read-Only Memory (ROM)

Read-Only Memory (ROM) is a type of memory that you cannot write to. Information is written to ROM chips by the manufacturer, and this information cannot be changed. In the past, if ROM information needed to be updated, you had to remove the original ROM chip and replace it with an updated ROM chip from the manufacturer. Today you can update the ROM by running a special software program downloaded from the manufacturer's Web site, which means that you don't really have a ROM chip - you have an EEPROM (more on EEPROM in a bit).

Software written to a ROM chip is called firmware. One of the major uses for ROM is storing the system BIOS (Basic Input-Output System), which contains Power-On Self-Test (POST) routines and other routines that initiate the loading of the operating system. The BIOS also contains the low-level code that allows the system to communicate with hardware devices.


Erasable Programmable Read-Only Memory (EPROM) is a type of memory that normally cannot be written to because it is a variation of ROM. An EPROM chip is a special ROM chip that the manufacturer can reprogram by using a special programming device that uses ultraviolet light.


A new implementation of ROM is called Electrically Erasable Programmable ROM (EEPROM), or flash ROM. The manufacturer writes the software instructions into the ROM chip, but you can update these instructions by running a special software setup program provided by the manufacturer. The software setup program is usually provided to you through the manufacturer's Web site.

EEPROM has become the typical way to update your BIOS. BIOS code is designed to work with certain hardware. As hardware improves, you need to update your BIOS code so that your system is aware of these hardware improvements. Therefore, the manufacturer places BIOS updates on its Web site for computer users running its particular BIOS to download. You just have to download the BIOS update program and then run the BIOS update on your system. The update rewrites the BIOS instructions, making the computer "more aware" of today's hardware.

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