View source for Read-only memory

'''ROM''' is simply '''Read Only Memory'''.

Unlike [[Random Access Memory|RAM]], ROMs cannot be written to. At one point, ROMs are also typically slower than RAM.

ROMs come in several flavors:

== PROM ==

PROMs can be programmed ONCE then read many times.  If there are any mistakes in the PROM code, the entire chip must be discarded.  While PROMs can be read in a normal board, they need to be programmed in a special device (since programming them often requires special [[voltage]]s).

== EPROM ==

[[Image:M27C512 EPROM.jpg|150px|right|An EPROM]]

EPROMs can be erased after they have been programmed.  Normally there is a small window in the chip in which exposure to UV light will erase the EPROMs programming.  EPROMs also need to be programmed in a special programmer.

== EEPROM ==

EEPROMS can be erased electronically, and re-programmed, usually through the application of higher than normal voltage. In modern EEPROMS this is generated internally. Unlike EPROMs, EEPROMS can be re-written in-circuit.

==External links==

* [http://madrona.ca/e/corerope/index.html Core Rope & Woven-Wire Memory Systems]

[[Category: Computer Basics]]