Sun 4/110 FPU

[Barry Lustig]

SYSRUTH at utorphys.bitnet (Ruth Milner) writes:
> The Sun 4 (all models) FPU is not an option, but an integral part of the
> CPU that does all floating-point operations. Sun 4's do not even support
> -fsoft, because the FPU is always there. If it dies, not even your kernel
> will run. Note that the man pages for cc and f77 mention this, and also
> that there is no place in the config. file to put an entry for one.

Wrong, wrong, wrong.  You can buy a 4/110 *without* floating point.  The
floating point on a 4/110 is provided by a pair of Weitek floating point
chips.  The floating upgrade costs $2,650.  If your machine doesn't have
floating point, the kernel provides software emulation of the floating
point instructions.  This differs with the Sun 3s, where the floating
point code is inserted, inline, into the user's binary.  We did some
simple benchmarks on a 4/110 with and without the floating point.  The
code we timed was some part of the GBRL ray tracing package.  In some
cases, the performance of the software floating point was as much as 200
times slower than with the hardware.

Barry Lustig
Advanced Decision Systems	barry at ADS.COM

[[ Thanks to everyone else who contributed similar information.  --wnl ]]