Erasable ROM technology

EEPROMs and FlashRAM

The next evolution in ROMs came in the form of the Electrically-Erasable/Programmable Read Only Memory. Unlike EPROMs, which had to be erased via UV light exposure, EEPROMs could be erased electrically without removing the chip from the board and could still retain their information without having power applied to the chip.

All current computer BIOSes are stored on a variation of this type of EEPROM chip, which is commonly called a FlashRAM. The chip can be reprogrammed by means of a special "flash" program, which can be used to erase the current information, and then program new information into the chip. FlashRAM offers manufacturers a very cheap and easy way of upgrading their products without having to produce new parts. All the motherboard manufacturer needs to do is write the new code, bundle it with a flasher program and then make it available for download.

Two major drawbacks to FlashRAM exist; the first is that there is a possibility that a power surge can accidentally erase the chips. Simply removing the memory card before powering and shutting off the device will prevent accidents, but in most cases, the manufacturer has already taken steps to keep the memory safe, so the end user does not need to worry about accidental erasure. The second is that FlashRAM is also more expensive to produce. Currently, demand is outpacing supply

FlashRAM is the closest equivalent to a permanent, re-writable storage medium was to use a normal RAM chip with a battery backup. Many computers used this solution for storing CMOS information for years, and of course, if the battery died, the CMOS information would be lost. FlashRAM was the perfect solution, since not only the BIOS program itself could be store on the chip, but the user settings and hard disk parameters could be as well, ensuring that your computer always has the information that it needs to startup and operate.

While your computer still uses a battery, that battery only powers the RTC (Real Time Clock) chip, so if the battery dies, the only information lost is the time and date, which is not critical to the operation of the system, and can easily be reset as needed until a replacement battery is installed.