I have studied ArmV8, which is RISC architecture before. I know the assembly, and the pipelining, data forwarding, and other data hazard solutions like stalling and branch prediction.
But what is exactly is CISC? Like what does x86 assembly look like? Do things like pipelining, data forwarding still exist? If yes, then what exactly is the difference between RISC and CISC?
In: 4
RISC cpus will use simpler instructions. But internally, there’s not as much difference.
Basic Load/Store operations, Arithmetic, etc. Arithmetic operations operate only on registers.
On ARM:
ldr r1, [r4]
ldr r2, [r4+4]
add r0, r1, r2
str r0, [r5]
loads two values from memory,
adds registers r1 + r2 and stores to r0, then stores that to memory
x86 has different addressing modes, you can do register-register, register-memory, memory-register
it would look more like:
mov eax, [rbx]
add eax, [rbx+4]
mov [rdx], eax
So x86 saves an instruction, but internally it’s still executing similar lower-level instructions (microcode).
Yes pipelining, instruction reordering, etc definitely occur on CISC/x86 as well.
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