Summary

20 IT Essentials: PC Harware and Software Companion GuideROMRead-only memory (ROM) chips are located on the motherboard. ROM chips containinstructions that the CPU can access directly. ROM stores basic instructions for booting thecomputer and loading the operating system. ROM chips retain their contents even when thecomputer is powered down. The contents cannot be erased, changed, or rewritten by normalmeans. ROM types include the following:■■■Programmable read-only memory (PROM): Information is written to a PROM chipafter it is manufactured. A PROM chip cannot be erased or rewritten.Erasable programmable read-only memory (EPROM): Information is written to anEPROM chip after it is manufactured. An EPROM chip can be erased with exposure toUV light. Special equipment is required.Electrically erasable programmable read-only memory (EEPROM): Information iswritten to an EEPROM chip after it is manufactured. EEPROM chips are also calledflash ROMs. An EEPROM chip can be erased and rewritten without removing the chipfrom the computer.NoteROM is sometimes called firmware. This is misleading, because firmware is actually the softwarethat is stored in a ROM chip.RAMRandom-access memory (RAM) is the temporary storage for data and programs that arebeing accessed by the CPU. RAM is volatile memory, which means that the contents areerased when the computer is powered off. The more RAM in a computer, the more capacitythe computer has to hold and process large programs and files, as well as enhance systemperformance. The different types of RAM are as follows:■■■■Dynamic RAM (DRAM) is a memory chip that is used as main memory. DRAM mustbe constantly refreshed with pulses of electricity to maintain the data stored in the chip.Static RAM (SRAM) is a memory chip that is used as cache memory. SRAM is muchfaster than DRAM and does not have to be refreshed as often.Fast Page Mode (FPM) DRAM is memory that supports paging. Paging enables fasteraccess to the data than regular DRAM. Most 486 and Pentium systems from 1995 andearlier use FPM memory.Extended Data Out (EDO) RAM is memory that overlaps consecutive data accesses.This speeds up the access time to retrieve data from memory, because the CPU doesnot have to wait for one data access cycle to end before another data access cyclebegins.