If 64 bit CPU’s all run on a 64 bit x86 architecture, how are they getting faster?

Question

So my question is this, if all modern day computer CPUs (central processing units) more or less have the same or similar clockspeeds from generation to generation as of late, and all run on a 64 bit architecture with an x86 instruction set, what about the processor is being altered or changed to yield performance gains from one gen to the next?

I understand that more cache is available, and transistor sizes are getting smaller and smaller, but at the end of the day, it is still running an x86 instruction set at 64 bits.

So last gens 4 core 4.5 GHz processor should run identically as quickly as a current gen 4 core 4.5 GHz processor theoretically – but that is not the case.

In: Technology

Answer 1

The biggest problem with making current CPUs go faster is feeding them data to work on so they aren’t ever sitting idle. It doesn’t matter if they crunch the numbers in 1 five-billionth of a second if they don’t have the numbers on hand to crunch.

A lot of the Instructions Per Clock (IPC) gains in recent years have come from always having data for the CPU to work on. One common technique that modern CPUs have is that when a program is waiting on something to happen that requires a decision to be made, the CPU will guess what the outcome will be and start executing instructions based upon that guess. This is called branch prediction. The more accurately a CPU can guess the correct branch and the faster that it can reset from a mistake will speed up how much data it can process.

Also, as you alluded to, caches are really important. Having reliable access, quick access to the data means that the CPU spends less time waiting for data to be transferred. One of the big ways that the most recent generation of AMD processors sped up IPC was by making it so that more cores could access the same pool of cache memory. That way there is a higher likelihood that the data it needs is already in cache instead of having to be loaded.

There are a lot of other behind-the-scenes performance improvements that CPUs can implement that don’t involve changing the x64 instruction set.