AMD's Zen microarchitecture. At the time, AMD was years behind Intel in both performance and power consumption. There were constant jokes about the Bulldozer cores burning people's houses down. The few remaining 'team red' loyalists had been hyping Zen were largely ignored. Then, boom. Over night AMD leapfrogged Intel, and now on the third generation has a firm lead in mid range desk top all the way up to high end se…
There are two parts to the story: architecture and process. On architecture, AMD deserves praise. On process, not so much. They didn't "git gud," they gave up. Which clearly was the right move for them, don't get me wrong, but I think all this partying in the streets about the TSMC monoculture is... shortsighted.
To improve yields they used a number of 8-core "chiplets" manufactured in 7nm tied together with a 14nm I/O die. This meant that while a certain blue competitor was still trying to get 28+ core monolithic dies, AMD could scale to huge core counts without reducing yields by tying together more chiplets.
Their 64-core 128-thread Threadripper workstation parts should have yields almost exactly as good as their low-end CPUs. The Xeon W 28-core monolithic monster? Not so much.
AMD did a lot of things right this time. Intel's got some catching up to do.