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MEMORY
A computer's capacity for storing
information.
More Detailed Definition:
Internal storage areas in the
computer. The term memory identifies data storage that comes in
the form of chips, and the word storage is used for memory that
exists on tapes or disks. Moreover, the term memory is usually
used as a shorthand for physical memory, which refers to the
actual chips capable of holding data. Some computers also use
virtual memory, which expands physical memory onto a hard disk.
Every computer comes with a certain amount of physical memory,
usually referred to as main memory or RAM. You can think of main
memory as an array of boxes, each of which can hold a single byte
of information. A computer that has 1 megabyte of memory,
therefore, can hold about 1 million bytes (or characters) of
information.
There are several different types of memory:
- RAM (random-access memory): This is the same as main memory. When
used by itself, the term RAM refers to read and write memory; that
is, you can both write data into RAM and read data from RAM. This
is in contrast to ROM, which permits you only to read data. Most
RAM is volatile, which means that it requires a steady flow of
electricity to maintain its contents. As soon as the power is
turned off, whatever data was in RAM is lost.
- ROM (read-only memory): Computers almost always contain a small
amount of read-only memory that holds instructions for starting up
the computer. Unlike RAM, ROM cannot be written to.
- PROM (programmable read-only memory): A PROM is a memory chip on
which you can store a program. But once the PROM has been used,
you cannot wipe it clean and use it to store something else. Like
ROMs, PROMs are non-volatile.
- EPROM (erasable programmable read-only memory): An EPROM is a
special type of PROM that can be erased by exposing it to
ultraviolet light.
- EEPROM (electrically erasable programmable read-only memory): An
EEPROM is a special type of PROM that can be erased by exposing it
to an electrical charge.
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