Exactly how “fast” are modern CPUs?

Question

When I used to program embedded systems and early 8/16-bit PCs (6502, 68K, 8086) I had a pretty good handle on exacly how long (in nanoseconds or microseconds) each instruct

Answer 1

I don't think the worst case is bounded on some platforms. When you have multiple cores and processors vying for the same locations or adjacent memory locations you can see all kinds of degradation in performance. Cache lines have to get moved around from processor to processor. I've haven't seen a good worst case number for memory operations on modern platforms.