[rbanffy]

While not exactly a chip (it never reached board stage) I designed a processor in college where the register file was keyed to a task-id register. This way, context switches could take no longer than an unconditional jump.

I dropped this feature when I switched to a single-task stack-based machine (inspired by my adventures with GraFORTH - thank you, Paul Lutus). This ended up being my graduation project.