Subject: Re: Slightly Off-Topic...
To: Brad Spencer <>
From: Dave McGuire <>
List: port-alpha
Date: 06/26/2001 14:42:56
On June 26, Brad Spencer wrote:
>    Oh, come now.  What's wrong with the PCI bus?  It's vastly faster, and in 
>    many ways saner, than SBus.  And they've latched onto cheap, insanely 

  You mean the scaled-up versions of PCI are faster than sbus.  If
memory serves, original PCI is about the same speed as sbus, except in
certain situation where sbus is particular, the setup for
a transfer happens concurrently with the end of the previous transfer,
so data transfers can happen on every clock instead of wasting a bunch
of arbitration cycles in between.

  While I'm definitely a big fan of PCI, I think that Sun's move
(while not entirely bad) wasn't without its price.  Sure, sbus cards
are more expensive than cheap commodity PC parts.  But when I go to
sleep and put my pager on my nightstand, I'd rather not have cheap
commodity PC parts in the computer room, if you know what I mean.

  Call me weird, but there's just something that bothers me about using
the same ethernet card in your eight-year-old kid's disposable game PC
as in a $100K+ system in a multimillion dollar data center.

>    functionaly video cards and cheap hard drives for workstations (not for 
>    servers, of course). 

  "Cheaper" doesn't always mean "better".  The bus is nice, I will
agree...but the quality of manufacturing and the reliability of the
vast majority of PCI cards leaves a LOT to be desired.

>    Personally, I think Sun is spot on.  There's something to be said for 
>    economies of scale. 

  While I do agree, I don't think it was without a significant

> I don't know if this is still there, but when Sun first came out with the
> PCI based sparcs, there was a "warning", of sorts, on their own web page.
> If I recall properly, it stated that the buss speed would be about the
> same, even though the PCI buss is faster.  Something to do with interrupt
> latency, or some such.

  As I mentioned above, though I don't have the details, this has
something to do with overlapping arbitration and setup cycles with
data transfer cycles.  This reportedly allows real non-bus-overhead
data to be transferred on each cycle, with one transfer beginning at
the very end of the previous transfer with no intervening crud.

          -Dave McGuire