Re: Always an important consideration
Yeah, it was the untrappable interrupt.
No, it wasn't. On the original IBM PC the NMI (Non-Maskable Interrupt) was used for memory parity errors. Control-Alt-Delete was implemented in the BIOS keyboard code. You can find it easily if you have the IBM PC Technical Reference.
That also meant that in the DOS days you could easily intercept Control-Alt-Delete by changing the interrupt vector for the keyboard. My first non-trivial assembly program for the PC was a keyboard-enhancement TSR that hooked the keyboard interrupt, did things like key remapping and macro expansion, and then jumped back into the BIOS at the correct location (depending on what it was doing). I don't think it intercepted CAD, but it could have.
Biting the hand that feeds IT
