AGP, vs PCI, and throw in a little UPA was Re: [SunRescue] NetBSD v. Linux v. Solaris 2.51

[Christopher Byrne]

James Lockwood Sent: Wednesday, December 06, 2000 23:41

>The Sun PCI implementations also offer multiple PCI busses.  On the Ultra
>5 and 10 the second 32-bit/33MHz bus is used only for onboard devices
>(thus avoiding contention with expansion cards) but all other Sun PCI
>based systems offer at least 2 separate busses for cards (the AXi has 2
>groups of 3, for example).

The multiple bus architecture certainly greatly improves resource allocation
over the standard PC implementations, especially for those systems which
have 64 bit slots, but it doesn't change the fact that with todays ultra
high bandwidth devices, PCI is still a big limitation.

Moving to 64 bit and 66 mhz helps a lot, increasing maximum bandwitdh to
about 500 MB/s, but that is stil inadequate for the upcoming generation of
I/O controllers with speeds into the Gigabyte per second (FC-AL is expected
to be available at that speed within 18 months). What we really need is a
revolutionary rather than evolutionary jump in peripheral and component
interfaces. Some people are suggesting that serial I/O is the way of the
future, but I don't find myself convinced.


>It also causes significant memory contention issues when used in this
>manner with small-cache processors.  SGI worked around this with a faster
>hybrid memory bus in both the O2 and Visual Workstations.
>
>On-card texture memory is always faster when you can have enough.  The SGI
>IR2 is living proof of this (expensive) memory model.  UMA models will win
>when texture cache-busting occurs, or when texture data is highly dynamic.

Oh I definitley agree that dedicated texture memory is both far faster, and
far more expensive than UMA. SGI has made it very clear with the market
positioning of the O2 vs. the Octane how it views UMA workstations. Of coure
much of that difference is in marketing, and some is the ability to have a
second processor card, but the rest is made up with the large amount of high
speed texture memory in the Octane (up to 104mb, with 24mb of ffb RAM)

>The current max is 120MHz, available for 2 years:

Which machines have 120mhz UPA slots? The U80 only has 112.5 (of course it
does have two of them), and I cant find UPA speed specs on all systems

Chris Byrne