dgh@sun.com (David Hough) (04/24/89)
ucdavis!caldwr!rfinch@ucbvax.berkeley.edu inquires why the new FPU2 for Sun-4's is only available for new 4/260 systems and is not available as an upgrade for older systems. FPU2 does not work reliably with some fraction of existing 4/260 CPU's. Certain CPU components that are within tolerance when used with the previous FPU become marginal with the extra load represented by the FPU2 daughter board. In addition, the CPU board also requires mechanical changes to become double height to allow room for the daughter board. FPU2 implies you lose slot 2 on 4/260; the configuration guide has advised against using slot 2 for some time for thermal reasons. The result is that an unknown but significant percentage of existing systems can only be reliably upgraded to FPU2 by replacing the CPU board. This certainly changes the economics of the upgrade! You can't establish an upgrade price if you don't know what fraction of CPU boards require replacement. Ralph asks what customers can do about this. If I were a large self-sufficient Sun-4 site that can accept the risk of swapping components around I'd proceed as follows: order a new 4/260 with FPU2. Try removing the FPU2's from the new systems and installing in the older ones. Run them intensively for several days to see how many of the old CPU's work reliably with FPU2. Then approach your Sun sales person and indicate how many 4/260 FPU2 daughter boards you would buy if you could, and that you promise not to complain if they don't work in a particular older CPU. There's no guarantee that Sun would respond, but if several major customers got their sales people excited about this that would improve the chances of something happening. This procedure only works for people that routinely swap boards around their systems. I doubt that you would be covered by any warranty if you mess up or if an older CPU turns out not to work with FPU2 (it's possible that it would appear to work for a while). FPU2 does offer some remarkable performance improvements for certain types of applications. Ray tracing in geometrical optics is one good example; it has lots of sqrt's. One such benchmark is over 3X faster when recompiled with Fortran 1.2 and executed on FPU2, relative to Fortran 1.1 and FPU.