4. CISC vs RISC

So which approach is better?

These are the two ideas

CISC cpu

RISC cpu

The answer: It depends.

If the software involves many basic calculations and compares, the RISC approach may be the better (faster) solution.

On the other hand, if the software has a heavy emphasis on complex mathematics, then the CISC approach is probably better.

There are vendors who provide the CISC solution such as Intel and AMD and there are vendors who provide the RISC solution such as ARM.

It is not purely RISC or CISC however. For example the latest Intel CISC chips include a significant amount of RISC ideas within the cpu itself. This internal design is not visible to any compiler, but the advantages of a RISC approach is appreciated and used to improve performance whilst being able to run code (x86) from 35 years ago with the original 8086 cpu.

Comparison

CISC	RISC
Has more complex hardware	Has simpler hardware
More compact software code	More complicated software code
Takes more cycles per instruction	Takes one cycle per instruction
Can use more RAM to store intermediate results	Can use less RAM movements as there are more registers available
Compiler can use a single machine instruction	Compiler has to use a number of instuctions
Uses less RAM to store a program	Has to use more RAM as it uses more instructions
Legacy - there is about 40 years worth of coding that still needs to run on a cpu.	The historic need to run previously coded software is much less.

Challenge see if you can find out one extra fact on this topic that we haven't already told you

Click on this link: CISC and RISC processors