Architecture 01

Question 1

What is the fetch execute cycle?

Answer 1

This is how a processor accesses and performs steps of a program.

1. Load data from memory address in instruction pointer (ip)
2. Adjust the ip to refer to the next instruction
3. Control unit decodes data as an instruction
4. Instruction is carried out (e.g by ALU)
5. (Some instruction changes ip)

Question 2

What is an Instruction Set Architecture?

Answer 2

An ISA is a set of operations the hardware recognises, where each operation is an instruction and on each iteration of a fetch-execute cycle a processor executes an instruction.

Question 3

Past Paper Question: Give an advantage and disad- vantage of a long-lived ISA over generations of chip have over separate ISAs for each chip.

Answer 3

Advantage: Long-lived ISA’s have backwards compatibility and have been thoroughly tested and used
Disadvantage: The same interface must be used for each chip so not huge amounts of room for significant changes

Question 4

Past Paper Question: Describe in words what this instruction does:

imulq $44, (%rbx), %rax

Answer 4

Get the signed integer 64 bit value stored at the memory address in register rbx, multiply it by 44, and put the result in register rax