Re: S/360

multicsfan wrote:

> The 360/91 wasn't the only one with problems.  When I played with the 
> Watfiv source there were comments here and there about problems 
> different model 360's had.  Some were in error trapping.  I don't 
> remember which model(s) (I still have the printed source), but some of 
> them wiht pipelines could not accuratly re****t what instruction caused 
> an error, just that it was one of the ones in the pipe that caused the 
> problem.

> I believe some other early pipelined machines had this problem or even 
> worse ones.  not only did they have problems with error tracing during 
> execution but sometimes the program counter wasn't properly tracked 
> during normal interrupts like I/O, timers, etc.

Imprecise interrupts.

Some other processors had imprecise interrupts for things like 
protection, but the 360/91 and /195 had them for many of the floating 
point operations.  With out of order execution and completion, it
must complete all instructions before the interrupt can be taken.

PL/I (F) has a message that changes when sysgenned for the 91,
such that messages say NEAR when indicating where the error occurred.
Though with the STMT option it will put BR 0 instructions between each
statement to flush the pipeline. (And slow everything down.)

-- glen