The Complex Instruction Set Computer (CISC) based processors dominate the proces

Question

• The Complex Instruction Set Computer (CISC) based processors dominate the processor market over Reduced Instruction Set Computer (RISC) based processors despite the fact that RISC processor design reduces the instruction sets size and complexity to increase raw speed in fetching and executing instructions. RISC-based systems are used in portable devices, home automation, medical devices, and in robotics. Describe at least five reasons that allow CISC processors to dominate the market. Select the processor type you prefer and explain why.

• The system clock is a digital circuit that generates timing pulses, or signals, and transmits the pulses to other devices in the computer. The CPUs fetch and execution cycles are timed according to this clock. The signal is an electrical signal. Suppose that the signal is a light pulse or radio wave. Explain how this could be done if it were possible. If you believe that it would be impossible, explain why.

Explanation / Answer

A ) As it is quite evident, RISC is used on mainframes and by many high performance machines owing to the fact that the instructions are executed within one clock cycle. The only roadblock to RISC architecture was the larger amount of code required to do a task which could be achieved in very few lines on a CISC based processor. But times have changed and RAM has become a lot cheaper than it was 10-20 years ago leading to an revival of the RISC architecture.

The reasons why CISC became so popular and is something one would prefer are as follows:
1. CISC has made microprogramming as easy as Assembly programming. ( no LOAD and similar commands )
2. Fewer number of lines and hence reduced code size.
3. Given it how fast processors are now-a-days, the difference in the clock cycles has been blurred to an extent that there is hardly any difference between RISC and CISC architectures for trivial tasks.
4. Backward code compatibility as the new instructions are a superset of the old instructions.

B ) The way processors work, they require electric signals to control the behaviour of the transistors and the gates to achieve the desired result/output. If the electric signal were to be replaced by light signals, it would require the circuitry to be composed of photosensitive devices which would be cumbersome and prone to errors since sensitivity would be very less. Similarly, radio waves would not be suitable as system clock control signals.

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