Yes, that familiar little PC peripheral. The one that toggles a single keyboard/mouse/display ensemble between two or more connected machines.

They've quietly vanished from the market. And the fact appears to be discussed nowhere on the Net, at all. So I have seen it fit to make a note of it here.

What's this, you say, they are still available? I'll bite: who and where sells a KVM box that reliably works with recent ( 3840 × 2160 x 60 Hz ) display, and costs less than simply adding another such display would cost?

Every single claimed counterexample I've turned up, either has a kilometer of "this is rubbish, doesn't work at all at the claimed 4K res" reviews hanging from it; or no reviews at all, on account of no one being stupid enough to purchase a KVM that costs more than adding two or three additional high-quality displays to the workstation.

I have no idea re: just why the KVM has gone into extinction. But it seems to have! And said demise is rather difficult to explain in purely technical terms, because signal switches with arbitrary bandwidth remain available: analogue relays (as found in, e.g., inexpensive oscilloscopes and elsewhere.) So what gives?