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Unformatted text preview: l it encounters a check instruction that matches the speculative load. If the
load is valid, the system behaves as if the exception never happened.
Speculation technique combined with predication technique gives the compiler more
flexibility to reorder instructions and increase parallelism.
Notice that all the three techniques are based on the availability of an intelligent compiler
and closed coupling between the compiler and the processor. Hence the performance of
processors based on EPIC technology comes from both hardware and software.
THE MAIN MEMORY
We saw in the discussion above that the CPU contains the necessary circuitry for data
processing and controlling the other components of a computer system. However, one
thing it does not have built into it is the place to store programs and data that are needed
during data processing. We also saw that the CPU does contain several registers for
storing data and instructions, but these are very small areas that can hold only a few bytes
at a time and are just sufficient to hold only one or two instructions and the corresponding
data. If the instructions and data of a program being executed by the CPU were to reside
in secondary storage like a disk and fetched and loaded one by one into the registers of
the CPU as the program execution proceeded, this would lead to the CPU being idle most
of the time because there is a large speed mismatch between the rate at which CPU can
process data and the rate at which data can be transferred from disk to CPU registers. For
example, a CPU can process data at a rate of about 5 nanosecond/byte and a disk reader
can read data at a speed of around 5 microsecond/byte. Thus, within the time in which the disk can supply one byte of data, the CPU can process 1000 bytes. This would lead to a
very slow overall performance even if the computer system used a very fast CPU. To
overcome this problem, there is a need to have a reasonably large storage space, which
can hold the instructions and data of the pro...
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This document was uploaded on 04/07/2014.
- Spring '14