Processors And Memory

Part 4 - Read Only Memory

Read Only Memory - ROM is a special type of memory in which data is written onto a chip during manufacturing. Information strored to ROM is permanent and cannot be changed. The System ROM stores the BIOS - Basic Input/Output System, which is the set of instructions that a computer uses during the first stages of power up and initialization. With out the BIOS, the computer would not have a way to verify that the main hardware components, such as the hard drive, floppy drive, mouse, CD-ROM etc., are installed and working properly.

ROM - Types

PROM- Programmable ROM is a special type of memory chip that is manufactured without any configuration. Manufaturers can then "burn in" or program the chip to contain whatever type of configuration and information is needed.

Erasable Programmable Read Only Memory - EPROM maintains its contents and information without the use of electrical power. The stored information of an EPROM chip is erased by removing a protective cover and using special equipmant to reprogram the chip. EPROMs are usually erased using Ultra Violet light.

Electrically Erasable Programmable Read Only Memory - EEPROM - Similar to the EPROM, It is prograamable through a process known as Flashing. Commonly the system BIOS and other similar devices are forms of EEPROM. The Information that that is stored in EEPROM is known as Firmware. EEPROMs are used in many devices, including Modems, NICs, Hard drive Controllers, and even some Hard Drives, and CD Rom Drives to enable them to have Funnctionality Upgrades.

Electrically Alterable Read Only Memory - EAROM - Similar to the EEPROM in functionality, but does not require you to actually Erase all its contents before reprogramming. The tendency is to make changes to only certain parts / values. This behaviour is very similar to RAM, and is usually associated with the term Non-Volatile Random Access Memory - NVRAM. EAROMs usually tend to be Complimentary Metal-Oxied Silicone - CMOS chips, which still require minute amounts of power to keep their information. This is why Most computers will have some form of a CMOS Battery, to preserve this data. It also makes it much easier to clear the CMOS in case of incorrect configuration by just removing the Battery