The execution time of a program depends on the following:
| IC: the instruction count i.e., the number of instructions
executed in the program
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| CPI: the number of clocks needed for execution per instruction
|
| τ: the clock period
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Thus, the execution time of a program, T, can be expressed as:
T = IC x CPI x τ
To reduce the execution time of a program, this can be achieved
through one of the following:
| 1. Reduce the number of in the instructions in the program.
|
| 2. Reduce the number of clocks required for executing each
instruction.
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| 3. Reduce the clock period.
|
Reducing the number of instructions in a program is the task
of the programmer or compiler. Reducing the clock period can
be achieved mainly by using a fast implementation technology.
However, the number of clocks required for executing each instruction
can be reduced by using multiple-bus CPU organization.
Next, we will see two-bus and three-bus CPU organizations and
their impact on reducing the number of clocks required for
instruction execution.