Cisc Vs Risc

Question 1

What is an instruction set?

Answer 1

Set of all instructions written in machine code that can be recognised and executed by a given processing unit/ CPU

Question 2

CISC features

Answer 2

Used in laptop/ desktop computers. X86 processors made mainly by Intel and AMD
More complex hardware
Larger number of complex instructions of variable length
Multiple machine/ clock cycles per instruction
Physically larger, more complex circuitry, requires more silicon to make, typically more expensive
Greater energy consumption
Can’t make use of pipelining
Emphasis on hardware, compiler (software) does less work
Small code sizes, higher cycles per second
Makes more efficient use of RAM than RISC
Multiple addressing modes available

Question 3

RISC features

Answer 3

Used in smartphones, tablets, embedded systems. Made popular by ARM processors
Simpler hardware
Smaller number of simple, standardised instruction that are fixed length
Single machine cycle per instruction
Smaller in size, less complex circuitry required, less silicon, typically cheaper to produce
Lower energy requirements
Can support pipelining
Emphasis is on software, compiler has to do more work
Large code sizes, lower cycles per second
Heavy use of RAM (can cause bottlenecks if RAM limited)
Fewer addressing modes available