Hardware

An exponential speedup for factoring and discrete log, killing RSA and ECC; and only a square root for unstructured search, which is why symmetric crypto survives...

Erasing one bit costs kT ln 2 joules, unavoidably. The point where information theory becomes physics.

The constant factors that dominate asymptotics in practice, and cache-oblivious algorithms as the theoretical response.

Your hardware and compiler reorder your program. What, fences, and acquire/release actually guarantee.

Atomic registers cannot implement consensus for two threads; compare-and-swap does it for any number. Why your CPU has CAS.

An actual, unconditional circuit lower bound. Proof that lower bounds are possible at all, which is what stops The barriers: relativization and natural proofs from...

An unknown quantum state cannot be copied, and the two-line proof is just linearity.

Sample above twice the bandwidth or lose information irrecoverably.

How many errors you can fix given how much you're willing to pay in redundancy.

One machine simulates all others. Interpreters, VMs, and the stored-program computer are all this one theorem.