[Simh] PDP-11 MARK

[Johnny Billquist]

On 2018-08-02 02:26, dave porter wrote:
> Not really a simh question, but this might be an appropriate
> bunch of people.  What actually used MARK on PDP-11?
> 
> I think I recall that some Fortran system (F4P?) used it,
> but that's a vague feeling at most.
> 
> Certainly as a Macro-11 kernel-mode weenie, I never
> felt the need.

As far as I know, nothing used MARK.
It's ugly in that it requires that I-space and D-space overlap, at least 
for the stack, for it to work.
I once heard a rumor that DEC only came up with it to extend some 
copyright or patent a few more years, but I'm not sure there is much 
truth in that.
Anyway, it was an attempt at having a return mechanism for routines that 
cleaned up the stack, in a time where you did not have a frame pointer.

   Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol