Comment by mikepavone

> An important non-obvious detail for AMD is that they (at least in the past, I assume for this as well) have kept the instruction timings similar from generation to generation of consoles.

What? The Jaguar-based CPU in the PS4 has both a much lower clock and substantially lower IPC than the Zen 2 based one in the PS5. The timings are not remotely the same and the micro-architectures are quite different. Jaguar was an evolution of the Bobcat core which was AMD's answer to the Intel Atom at the time (i.e. low cost and low-power, though it was at least an out-of-order core unlike contemporary Atoms).

Going from GCN to RDNA on the GPU side is also a pretty significant architectural change, though definitely much less than the going from AMD to Intel would be.

I did some more research and I was wrong.

My source was an AMD tech talk from years ago where they mentioned keeping instruction timings the same for backwards compatibility reasons.

I believe they were talking about this for the XBox One X: https://en.wikichip.org/wiki/microsoft/scorpio_engine#Overvi... (and a similar chip for the PS4 Pro)

So basically, they upgraded and lightly enhanced the Jaguar architecture, shrunk the process (28nm -> 16nm), but otherwise kept it the same. AMD Zen was released around this time and was far superior but they decided to stick with Jaguar in order to make sure that instruction timings were kept the same.

I guess that they didn't want two hardware revisions of the same console generation running on different micro-architectures, but they were okay switching the micro-architecture for the next console generation.