https://www.anandtech.com/show/11550/the-intel-skylakex-review-core-i9-7900x-i7-7820x-and-i7-7800x-tested/6

That shows the latest Intel Skylake 28-core design has a 698 mm^2 die size. If you reduce the complexity of that design by a factor of 1,000 you have a chip smaller than 1 mm^2.

I know performance doesn't scale linearly with die size, but as a first approximation you could fit the performance of a high-end server in a microSD card.