This memory
uses Metal Oxide Semiconductor Technology. RAM is read-write memory whereas ROM
is Read-Only-Memory. This memory is used to store frequently used programs in
the system.
ROM can be
further divided into PROM, EPROM and EEPROM.
RAM
and ROM
In Case of RAM
it is possible to randomly select and use any Location of this memory. Each
memory Location can be as easily and speedily accessed as any other Location in
memory, that is, it takes the same access time wherever the Location in the
memory. It is possible to read from and write into this memory and hence this
memory is also called read/ write memory.
A
Read-Only-Memory is one in which information is permanently stored. This memory
cannot be written into. It can only be read. When power is switched off, the
contents of ROM remain unchanged. The manufacturers supply ROM chips along with
the programs therein. A variation of ROM chip is PROM.
The PROM can be
programmed to record information using a special facility known as PROM
programmer. But, once it is programmed using this facility, it becom,2s a ROM.
PROM is also
non-volatile.
However, there is another type of memory chip called EPROM which can be
reprogrammed several times. It is possible to erase information stored in
E:'ROM chip by exposing
it to
ultraviolet light and reprogram it using a special PROM programmer facility.
1. PROM
Programmable read-only memory can be programmed once. Special
circuitry is used for programming it. Once programmed, this becomes read-only
memory (ROM).
2. EPROM
Erasable programmable read-only memory can· be erased repeatedly
and reprogrammed by the us·=r. Erasing is done by exposing EPROM to ultraviolet
light of a specific frequency. Reprogramming requires special EPROM Programmer
kit.
3. EEPROM
Electrically
erasable programmable read-only-memory can be erased electrically and reprogrammed repeatedly.
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