and rowhammer etc mitigations microcode updates

personally I have an i7 in the lab that turned into a crawl on Youtube because they started sending VP9 video by default, but i7 doesn't have hardware decode for it. Got a plugin to force h264 (h264ify) and it's back to normal.

Then you have situations where a software update adds a CPU instruction dependency and straight up doesn't work anymore.

Had to install and force-retain an old version of Spotify client on a bench lab PC because the new versions require AVX-1/2. It's a streaming audio player...