30Jul MEMORY UNITS

All computers need a place to temporarily store information while other pieces of informations are being processed.In digital computers,information storage is normally conducted at two different stages:primary memory (made up of semiconductor RAM and ROM chips) and mass storage (usually involving floppy and hard disk drives). Most of teh system’s primary memory is located on the system board and typically exists in two or three forms: Read Only Memory (ROM)- which contains the computer’s permanent start up programs. Random Access Memory- which is quick enough to operate dirctly with the microprocessor and can be read from and written to as often as desired. Cache memory-which a fast RAM system uses to hold information that the microprocessor is likely to use. ROM devices store information permanently and are used to hold programs and data that do not change.RAM devices only retain the information stored in them as long as electrical power is applied to the IC.Any interruption of power will cause the contents of the memory to vanish.This is reffered to as volatile memory.ROM,on the other hand,is nonvolatile. Every system board contains one or two ROM ICs that hold the system’s Basic Input/Output System(BIOS) program.The BIOS program contains the basic instructions for communications between the microprocessor and the various input and output devices in the system.Until recently,this information was stored permnently inside the ROM chips and could only be changed by replacing the chips.

Advancements in EEPRROM technology have produced flash ROM devices that enable new BIOS information to be written (downloaded) into the ROM  to update it.This can be done from an update disk,or it can be downloaded from another computer.Unlike RAM ICs,the contents of the flash ROM remain after the power has been removed from the chip.In either case the upgraded BIOS must be compatible with the system board it is being used with and should be the latest version available.