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Read-Only Memory
Read-only memory (ROM) works like the name implies—it’s memory
the PC can read but can’t change (no writing allowed). The contents of
a standard ROM chip are burned in at the factory, and the end user
simply cannot alter it. ROM chips often contain “bootstrap”
information that computers use to start up prior to loading an
operating system from disk. This includes the familiar power-on self-
test (POST) series of diagnostics that run each time you boot a PC.
ROM’s primary advantage is that it can’t be modified. There is no
chance that user or administrator error will accidentally wipe out or
modify the contents of such a chip. This attribute makes ROM
extremely desirable for orchestrating a computer’s innermost
workings.
There is a type of ROM that may be altered by administrators to some
extent. It is known as programmable read-only memory (PROM), and
its several subtypes are described next:
Programmable Read-Only Memory (PROM) A basic
programmable read-only memory (PROM) chip is similar to a ROM
chip in functionality, but with one exception. During the
manufacturing process, a PROM chip’s contents aren’t “burned in” at
the factory as with standard ROM chips. Instead, a PROM
incorporates special functionality that allows an end user to burn in
the chip’s contents later. However, the burning process has a similar
outcome—once data is written to a PROM chip, no further changes are
possible. After it’s burned in, a PROM chip essentially functions like a
ROM chip.
PROM chips provide software developers with an opportunity to store
information permanently on a high-speed, customized memory chip.
PROMs are commonly used for hardware applications where some
custom functionality is necessary but seldom changes once
programmed.
Erasable Programmable Read-Only Memory (EPROM)
Combine the relatively high cost of PROM chips and software
developers’ inevitable desires to tinker with their code once it’s written
