alt Hacker NewsI suspect the shadow registers were there to improve interrupt handling, reserve their use exclusively to an interrupt handler, and you could save time in not having to store registers in memory.
I suspect the shadow registers were there to improve interrupt handling, reserve their use exclusively to an interrupt handler, and you could save time in not having to store registers in memory.
That, or in general for system calls. In particular EX AF,AF' + EXX allowed you to exchange all registers other than AF, to be able to return an error code or status.