[ILUG] bus bandwidth...

[David Murphy]

Quoting <19990923121025.C32752 at tuatha.org>
by "John P . Looney" <valen at tuatha.org>:

> PCI is supposed to be 32bit 33Mhz. That's 133 MB/sec, theoretical
> max.  SBUS (Sun's pre-pci bus) is 25MB/sec, proven.

Really? Proven by what, exactly? Sun quote the SBUS bandwidth at
100MB/sec for 32-bit SBUS, 200MB/sec for 64-bit SBUS, theoretical
maxima, of course.
Check out their PCI:SBUS comparison at
http://docs.sun.com:80/ab2/coll.28.17/SBUSPCICMP/@Ab2TocView?

> The Sun Enterprise 10000, which is a modified cray machine uses
> SBus. I've seen these machines with loads of gigabit network cards,
> fiberchannel cards etc. plugged into them. What's the point, if you
> only get 25 MB/sec into the machine ?

There wouldn't be, if that were true ;)

> Something is really odd here. Is SBus really that bad, or does PCI
> perform a lot worse under real conditions ?

> OK, I know that Sun are shipping machines with 64bit 66Mhz PCI, but
> the big iron machines aren't going to see that bus for two years or
> so...

Actually, you can get a PCI module for your 10000, if you want.

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