Curiosity

[Henry Spencer]

>	What the #%$@ does the MARK instruction do??!?

The fast answer is "nothing useful".  More specifically, it was an
attempt at making stack cleanup after procedure calls easier.  It was
so fearfully botched that nobody has ever found a real use for it.
In fact, it is difficult to understand how anyone would think it was
useful at all.  My personal guess is that it was intended to speed up
some bizarre interpretive implementation of some language.  (This sort
of thing is not unknown elsewhere; the reason why the System V IPC
stuff is such a kitchen-sink mix of different approaches is that it's
the union of the wishlists of several major AT&T internal projects.)
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry