Page 27 - DCAP104_EXPOSURE_TO_COMPUTER_DISCPLINES

Exposure to Computer Disciplines

Notes address of the cell and it is used to identify the cells. The address starts at 0 and goes up to
(N-1). You should know that the memory is like a large cabinet containing as many drawers
as there are addresses on memory. Each drawer contains a word and the address is written
on outside of the drawer.
(a) Capacity of Primary Memory You know that each cell of memory contains one character
or one byte of data. So the memory capacity is defined in terms of byte or words. The relation
is: 1 kilobyte (KB) = 1024 bytes. Thus 64 kilobyte (KB) memory is capable of storing 64 ×
1024 = 32,768 bytes. The memory size ranges from few kilobytes in small systems to several
thousand kilobytes in large mainframe and super computers. In your personal computer
you will find memory capacity in the range of 32 MB, 64 MB and even 128 MB (MB = Million
bytes and 1 MB = 1024 KB).
The following terms related to memory of a computer are discussed below:

2.3.1.1 Random Access Memory (RAM)
The primary storage is referred to as random access memory (RAM) because it is possible to
randomly select and use any location of the memory directly for storing and retrieving data. It
takes same time to reach any address of the memory whether it is in the beginning or in the last. It
is also called read/write memory. The storage of data and instructions inside the primary storage
is temporary. It disappears from RAM as soon as the power to the computer is switched off. The
memory, which loose its contents on failure of power supply, are known as volatile memories.
So now we can say that RAM is volatile memory.

Figure 2.4: RAM

2.3.1.2 Read Only Memory (ROM)

There is another memory in computer, which is called Read Only Memory (ROM).
Again it is the ICs inside the PC that form the ROM. The storage of program in the ROM
is permanent. The ROM stores some standard processing programs supplied by the
manufacturer to operate the personal computer. The ROM can only be read by the CPU
but it cannot be changed. The basic input/output program, which is required to start and
initialize equipment attached to the PC, is stored in the ROM. The memories, which do
not loose their contents on failure of power supply, are known as non-volatile memories.
ROM is a non-volatile memory.

Give the difference between RAM and ROM.

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