The basic performance equation is
$CPU time=Instruction count x CPI x Clock cycle time$,
in which the factor Clock cycle time can be affected by
- (a) ?Machine language.
- (b) ?Cycles per instruction.
- (c) ?Instruction level parallelism.
- (d) ?Instruction set architecture.
The Correct Answer and Explanation is :
The correct answer is (d) Instruction set architecture.
Explanation:
The basic performance equation for a computer system is:
[
\text{CPU time} = \text{Instruction count} \times \text{CPI} \times \text{Clock cycle time}
]
Where:
- Instruction count is the number of instructions executed by the program.
- CPI (Cycles per Instruction) refers to the number of cycles it takes to execute each instruction.
- Clock cycle time is the time taken for one cycle of the CPU’s clock.
Impact of Instruction Set Architecture (ISA):
The Instruction Set Architecture (ISA) defines the set of instructions that the processor can execute. It includes how instructions are represented, what operations can be performed, and how they interact with the system. The ISA affects both the CPI and the Clock cycle time.
- CPI (Cycles per Instruction): Different ISAs have different complexities in terms of how many cycles it takes to execute an instruction. For example, complex instructions might require more cycles to execute, resulting in a higher CPI. A RISC (Reduced Instruction Set Computing) architecture, for instance, typically has a lower CPI because it uses simpler instructions, whereas a CISC (Complex Instruction Set Computing) architecture may have a higher CPI due to more complex instructions.
- Clock Cycle Time: The design of the instruction set also influences the clock cycle time. An ISA that requires more complex operations can result in longer clock cycle times since the hardware needs to perform more work per cycle. Simpler ISAs often allow for higher clock speeds and thus shorter clock cycle times.
Other factors:
- (a) Machine language: Machine language is directly related to the ISA but does not directly affect the clock cycle time.
- (b) Cycles per instruction: CPI itself is influenced by the ISA but is a distinct factor from the clock cycle time.
- (c) Instruction level parallelism: This can help optimize performance but does not directly affect clock cycle time.
Conclusion:
The instruction set architecture plays a pivotal role in determining both CPI and the clock cycle time, making it the correct answer.
Now, let me provide an image that visually represents the equation and how the factors interact.
Here is an infographic that illustrates the CPU performance equation and how the Instruction Set Architecture (ISA) affects both the CPI and clock cycle time. You can see how different components are connected and influence CPU performance.