A kilobyte is
1024 bytes, or 210 bytes??”roughly a thousand bytes. A megabyte is 1,048,576 bytes, or 220 bytes??”roughly
a million bytes. A gigabyte is 1,037,741,824 bytes, or 230 bytes??”roughly a billion bytes.
We hear larger prefixes occasionally, too. A terabyte is 1,099,511,627,776 bytes, or 240 bytes??”roughly a trillion
bytes. A petabyte is 1,125,899,906,842,624, or 250 bytes??”roughly a quadrillion bytes. Such numbers are so
large that their discussion usually accompanies speculation about the future of computing. However, we are starting
to hear about active data bases in the terabyte, and even the petabyte range (http://www.informationweek.com/
story/IWK20020208S0009).
Memory is used to store program instructions and data. The basic operations on memory are store and retrieve.
Storing is also referred to as ???writing.??? Retrieval is also referred to as ???fetching,??? ???loading,??? or ???reading.??? Fetch
is an obvious synonym for retrieve, but what about load? By loading one means loading a register in the CPU
from memory, which from the point of view of the memory system is retrieval.
There are at least two registers associated with the memory control circuitry to facilitate storage and
retrieval.
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