-=> Quoting Steven Horn to Greg Mayman <=-

 GM> To go back to my previous analogy of the security checks at the
 GM> airport, "stealing cycles" is analogous to the security personel
 GM> stopping you and checking you every step or so. This would cause a
 GM> massive slowdown.

 SH> But the analogy does not work, cycles are stolen while the program is
 SH> waiting for something. 

Depends. It's possible to tie the "monitoring" to interrupts or the
like. So unless that interrupt is called, the routine uses *no* cycles.
And when it is called, the OS or some driver would be using cycles
anyway. 

Heck, I was doing that sort of thing clear back in 1981 on a TSR-80
Model III. The keyboard, printer and serial port all did a call to
specific RAM addreses when called. You could replace the call there
with a call to your own routine that could then (after it did whatever
ryou needed it to do, could either pass stuff on to the BIOS routine or
just return to the program. 

I know that PCs can do similar things. 

I wrote something that was the equivalent of the PC's Alt- functionality on that old gear. Didn't use any cycles except when
entering stuff from the keyboard.

--- FMailX 1.60