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I'm trying to understand the difference between CISC and RISC architecture. I read this to understand the difference between CISC and RISC arhictecture but I'm confused.

There is a sentence in the article like that

MULT is what is known as a "complex instruction." It operates directly on the computer's memory banks and does not require the programmer to explicitly call any loading or storing functions

after that explanation, I examined MUL operations in RISC and CISC.

In CISC x86 architecture;

  mov ax, 5
  mov cx, 10
  mul cx

the result is stored in dx, ax registers.

In RISC PowerPC arhictecure;

li r0, 5
li r1, 10
mul r2, r1, r0

According to mul instruction explanation, the result is stored r2 and mq registers.

The instructions are same for two architectures in perspective of programmers. They are using same methodology for multiplying. How come we say one is RISC other is CISC ?

beginner_dv
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  • Difference between RISC and CISC is not about the MUL instruction, but about other stuff. If MUL instruction appears to be the same then that only means that the MUL instruction is simple enough. Some other instructions are complex and do not even exist in RISC. – Dialecticus May 27 '21 at 10:55

1 Answers1

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I think their point is that you can also give the CISC one a memory location as an argument.

See: https://www.felixcloutier.com/x86/mul

and the m16 .. m64 variants.

  • And IMUL has [even more fun variants](https://stackoverflow.com/questions/3860017/what-exactly-does-the-3-operand-imul-instruction-do-in-ia-32-assembly). –  May 27 '21 at 10:53