Page 44 - DCAP101_BASIC_COMPUTER_SKILLS

Unit 3: Memory

3.2.1 Random Access Memory (RAM) Notes

When people talk about computer memory, they usually mean the volatile RAM memory.
Physically, this memory consists of some integrated circuit (IC) chips (see Figure 1.1) either
on the motherboard or on a small circuit board attached to the motherboard. A computer’s
motherboard is designed in a manner that its memory capacity can be enhanced easily by
adding more memory chips. Hence, if you decide to have more memory than your computer
currently has, you can buy more memory chips and plug them in the empty memory slots
on the motherboard. Service engineers normally do this job. The additional RAM chips
which plug into special sockets on the motherboard, are known as single in-line memory
modules (SIMMs).

Figure 3.1: Random Access Memories (RAM)

3.2.2 Read-Only Memory (ROM)
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 usual programs. 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. 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, data stored in
a ROM are not lost when power is switched off or interrupted unlike in the case of a volatile
RAM chip. ROM is also known as field stores, permanent stores, or dead stores.
ROMs are mainly used to store programs and data that do not change and are frequently used.
Most basic computer operations are carried out by wired electronic circuits. However, several
higher-level and frequently used operations require very complicated electronic circuits for
their implementation. Hence, instead of building electronic circuits for these operations,
special programs are written to perform them. These programs are called micro programs
because they deal with low-level machine functions and are essentially substitutes for additional
hardware. ROMs are used by computer manufacturers to store these micro-programs so that
they cannot be modified by the users.
A good example of a micro-program is the set of instructions needed to make a computer
system ready to use when it is powered on. This micro-program, called ‘’system boot
program”, contains a set of start-up instructions to check if the system hardware like
memory, I/O devices, etc. are functioning properly. It looks for an operating system and
loads its core part in the volatile RAM of the system to produce the initial display-screen
prompt. Note that this micro-program is used every time the computer is switched on and
needs to be retained when the computer is switched off. Hence, ROM is an ideal storage for
storing it.

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