[timpattinson]

IBM had 5GHZ in 2014. [1] Clock speed is not a measure of performance alone.

Besides, most of the work in reaching a certain clock speed or target can be owed to the foundry (in this case TSMC which is world-leading, certainly beating Intel on most metrics at the moment.)

Comparing to the over-tuned enthusiast SKU of 2018 is not a fair comparison for either. Also 600W is not impossible to cool, there are GPUs at that level of power for a while now.

[1] https://en.wikipedia.org/wiki/POWER8

[rayiner]

IBM hit 5 ghz in 2008: https://en.wikipedia.org/wiki/POWER6. IBM’s Cell hit 4 ghz in 2006 on a 65 nm process.

[Symmetry]

The advantages of chopping up chopping your pipeline stages in half so that each is 10 FO4s long rather than the 16 FO4s most people use. You've generally got 2 FO4s of latching and 2 of clock skew so IBM was seeing 6 FO4s of useful work per stage compared to 12 with Intel. Or at least the overhead was 4 per stage in the mid 2000s, I've got no idea what they are in the early 2020s.

[rbanffy]

And, if you have enough threads per core, it's relatively simple to switch to another thread when an instruction stalls. Unfortunately, most our software is designed for machines with few fast cores.