Performance Considerations 
The execution time of a program depends on the following:
IC: the instruction count i.e., the number of instructions executed in the program
CPI: the number of clocks needed for execution per instruction
τ: the clock period

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.
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.