Turbo Boost can certainly apply to all cores- the limits you hit are TDP and time based, there, not strictly thermal.

So, for example, my old laptop CPU would clock itself up to 2.7GHz on all cores... well, okay, it was a dual core, so that's not saying much, but still. But it'd only maintain that boost for a few seconds- under sustained load it dropped down to 2.5. This wasn't because of thermals, but rather because 2.7GHz was a Turbo Boost frequency, and once the PPL timer runs out...

And to explain why they don't have, say, one core boost to 5.1GHz...well, let's see what siliconlottery says.

> As of 3/16/19, the top 38% of tested 9900Ks were able to hit 5.0GHz or greater.

> As of 3/16/19, the top 8% of tested 9900Ks were able to hit 5.1GHz or greater.

So, Intel'd cut their yield by more than a factor of four if they only let parts that could hit 5.1 into this bin. For a 2% single-core performance boost...

I think those numbers are for chips that can 5.1 GHz all core though, which is probably a lot less than 5.1 GHz single core.

As far as I know, K-series parts don't support binning of individual cores- if you have one bad core that'll only hit 5.0, 1-core turbo to 5.1 will still result in the OS scheduler periodically picking that core to use, it clocking up to 5.1, and problems resulting.

Might be wrong, though.

Intel's Turbo Boost 3.0 [1] was their attempt to take advantage of the fact that some cores on a chip can clock higher than others. It does not work well in practice, because it requires too much collaboration with motherboard and OS vendors. This feature is not available on their desktop platform, which the i9-9900KS uses.

[1] https://www.intel.com/content/www/us/en/architecture-and-tec...