Keyboard buffers are decidedly not on the physical keyboard. The keyboard might have a very small one, but the IRQ is triggered on every input. The buffer in q

Keyboard buffers are decidedly not on the physical keyboard. The keyboard might have a very small one, but the IRQ is triggered on every input. The buffer in question is, for a tty, a driver-level buffer that holds on to the data until something reads it. If a command doesn't read it (which things like apt-get update don't) then it'll get read as the next command. Of course, most terminals these days are ptys accessed via emulators, so the buffer is actually part of the emulator, but the same idea applies.