Accelerator boards - no future? Bad business?

[Sean Conner]

It was thus said that the Great Eric Smith once stated:
> On Fri, Apr 22, 2016 at 9:29 PM, Sean Conner <spc at conman.org> wrote:
> >   One major problem with adding a faster CPU to an SGI is the MIPS chip
> > itself---code compiled for one MIPS CPU (say, the R3000) won't run on
> > another MIPS CPU (say, the R4400) due to the differences in the pipeline.
> > MIPS compilers were specific for a chip because such details were not hidden
> > in the CPU itself, but left to the compiler to deal with.
> 
> Having written a bunch of R3000 and R4000/4200/4300/4400/4600 assembly
> code in the 1990s, my (possibly faulty) recollection disagrees with
> you. There are differences in supervisor-mode programming, but I don't
> recall any issues with running 32-bit user-mode R3000 code on any
> R4xxx. The programmer-visible pipelline behavior (e.g., branch delay
> slots) were the same.

  Hmm ... I might have been misremembering.  I just checked the book I have
on the MIPS, and yes, the supervisor stuff is different between the R2000,
R3000, R4000 and R6000.  Also, the R2000, R3000 and R6000 have a five stage
pipeline, and the R4000 has an eight stage pipeline.

> That's only considering the CPU itself, which I used as an embedded
> processor; I never used IRIX so I don't know whether IRIX on R4xxx
> might have somehow prevented use of IRIX R3xxx binaries (e.g., by
> different system call conventions or the like).

  That I do not know.  There were very few SGIs on campus at the time.

  -spc