Unformatted text preview: ot; or refresh the storage charge to retain the
stored data. On the other hand, a static RAM (SRAM) does not need any special
regenerator circuits to retain the stored data. Since it takes more transistors and other
devices to store a bit in a static RAM, these chips are more complicated and take up more
space for a given storage capacity than do dynamic RAMs. Moreover, a static RAM is
faster, costlier, and consumes more power than dynamic RAM. Due to these reasons,
large memories use dynamic RAM, and static RAM is used mainly for specialized
applications. The main memory of most computers uses dynamic RAM.
A special type of RAM, called read-only memory (ROM) is a non-volatile memory chip
in which data is stored permanently and cannot be altered by the programmer. In fact,
storing data permanently into this kind of memory is called "burning in the data", because
data in such memory is stored by using fuse-links. Once a fuse-link is burnt it is
permanent. The data stored in a ROM chip can only be read and used - they cannot be
changed. This is the reason why it is called read-only memory (ROM). Since ROM chips
are non-volatile, the data stored inside a ROM are not lost when the power supply is
switched off, unlike the case of a volatile RAM chip. ROMs are also known as field
stores, permanent stores, or dead stores.
ROMs are mainly used to store programs and data which do not change and are
frequently used. For example, the most basic computer operations are carried out by
wired electronic circuits. However, there are several higher level operations that are very
frequently used but will require very complicated electronic circuits for their
implementations. Hence instead of building electronic circuits for these operations,
special programs are written to perform these operations. These programs are called
microprograms because they deal with low-level machine functions and are essentially
substitutes for additional hardware.
Microprograms are written to aid the control unit in directing a...
View Full Document
This document was uploaded on 04/07/2014.
- Spring '14