We don't know anything about Apple's implementation, but for perspective, in Nvidia's first implementation of RTX RT cores occupied about 6-7% of the area of a TPC, where TPCs constitute the majority, but not the entire die, so it's an even smaller (but not by much) portion of the entire die. Maybe 5% or so.

It's possible that the latest gen of RT cores are a slightly larger portion of a TPC (but we don't know), but on the other hand, TPCs are a smaller portion of a die now as TPC arrays do not include L2, and L2 got many times bigger. So chances are, RT over die area is still somewhere on the order of 5%.

And in Nvidia designs as far as I understand RT cores sit idle in non-RT workloads, yes.

If anything, Tensor cores are almost twice as large as RT cores, and tensor cores sit idle whenever you don't use DLSS (or professional ML compute).

See https://www.reddit.com/r/hardware/comments/baajes/rtx_adds_1...