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Unformatted text preview: emory. Each drawer contains a word and the address of each word is
written on the outside of the drawer. If we write or store a word say 10101010 at address
125, it is like placing the word 10101010 in the drawer labeled 125. Later, reading from
address 125 is like looking in that drawer to see its contents which is now 10101010. We
do not remove the word at an address when we read, but change the contents at an
address only when we store or write a new word. Thus, entering data into a storage
location is destructive of previous contents, but retrieving data from a location is nondestructive. The act of entering data into a storage location is called memory write
operation, and the act of retrieving data from a storage location is called memory read
operation. Hence read is a non-destructive operation and write is a destructive operation.
Why More Bits?
You might have heard about 8-bit computers, 16-bit computers, 32-bit computers, etc.
This refers to the word length of the memory of a particular computer in terms of total
number of bits per memory word. Word length is an important architectural factor. Small
machines have word lengths of 8, 16, or 32 bits; large machine word lengths are 64 bits
or more. The obvious question that arises to ones mind is that what is the advantage of
having more number of bits per word instead of having more words of smaller size
For an answer to the above question, imagine a highway with eight lanes, and a heavy
flow of traffic. If it is expanded to sixteen lanes, the flow of traffic speeds up
considerably. "8 bits" refers to the number of "lanes" on a microchip. More bits means a
more rapid flow of electronic signals. In other words, a faster computer. Thus, what an 8bit computer takes one miriute to db, a 32-bit computer may do in few seconds.
Data and instructions are moved to and from memory in bunches of word length.
Therefore, even if the electronic circuits used are comparable in speed, machines having
smaller word-length will be slower in operation than machines having larger word-length.
This difference is analogous to providing the user of a machine having smaller word lengt...
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This document was uploaded on 04/07/2014.
- Spring '14