ROM, PROM, AND FLASH MEMORY

A special type of internal memory, called readonly memory (ROM), cannot be altered by the user (see Figure 2-5). The contents of ROM (rhymes with "mom"), a nonvolatile technology, are "hard-wired" (designed into the logic of the memory chip) by the manufacturer and can be "read only." When you turn on a microcomputer system, a program in ROM automatically readies the computer system for use and produces the initial display-screen prompt.
A variation of ROM is programmable read-only memory (PROM). PROM is ROM into which you, the user, can load read-only programs and data. Generally, once a program is loaded to PROM, it is seldom, if ever, changed. ROM and PROM are used in a variety of capacities within a computer system.
Flash memory is a type of PROM that can be altered easily by the user. Flash memory is a feature of many new processors, I/O devices, and storage devices. The logic capabilities of these devices can be upgraded by simply downloading new software from a vendor-supplied disk to flash memory. Upgrades to early processors and peripheral devices required the user to replace the old circuit board or chip with a new one. The emergence of flash memory has eliminated this time-consuming and costly method of upgrade. Look for nonvolatile flash memory to play an increasing role in computer technology as its improvements continue to close the gap between the speed and flexibility of CMOS RAM.