RE: PCI 2.3 and 5V signaling (was: PCI-X Compatibility)

["Austin Franklin" <darkroom@ix.netcom.com>]

Hi Andrew,

> PCI Revision 2.3 eliminates 5V plug-in cards, but does NOT
> eliminate 5V PCI motherboards.

This is what the PCI SIG said:

"Revision 2.3 supports the 5V and 3.3V keyed system board connectors (as did
revision 2.2) but revision 2.3 supports only the 3.3V and Universal keyed
add-in cards. The 5V keyed add-in card is not supported in revision 2.3."

> PCI Revision 2.3 eliminates only the 5V-only PCI plug-in cards.

Though the spec may in fact not "support" 5V plug-in cards, if the system
boards do support the 5V keying (as it says it does above, and you also
interpret it to, and I was hoping the reality really was), then it seems
like a moot point...  I understand the purpose of making this "part of the
spec", trying to phase out 5V plug-in cards.

> PCI Revision 2.3 continues to support 5V buses (motherboards),
> into which any Universal plug-in card or Revision 2.1 or 2.2
> compliant 5V-only card can be plugged.

That's what I was hoping the reality was, but that's not what was said.
Thank you very much for the clarification.  I'm glad I asked...

> If this caught you by surprise, then I don't know where you've
> been hiding.  The writing has been on the wall for years.

I never said the "move" to 3.3V "caught me by surprise".  What I said was,
if the 2.3 spec did NOT support the millions of 5V plug in cards that
already exist, that would be outrageous, IMO.  Apparently, according to your
interpretation, and a careful reading of the above quote, 5V plug in cards
are still supported by the motherboards in 2.3.

> Since
> 1995, the PCI Spec has been saying that everyone should be
> designing only Universal plug-in cards.  Yet it amazes me how
> many people still keep designing 5V-only plug-in cards in 2002
> ... seven years later!

Why are you so amazed at that?  People still design AND use ISA cards.
People still design and use Q-Bus cards...STD bus cards...etc.  There are
BILLIONS of dollars invested in "older" equipment that still works perfectly
well, and does the job perfectly well.

> Would you prefer that computer vendors simply start introducing
> systems with 3.3V PCI buses (because they can't make corelogic
> chipsets that can receive 5V signals), and instantly invalidate
> millions of 5V-only PCI plug-in cards that are already out there?

No.  That was my point.

> Or would you prefer to have years of warning, and a phase-in of
> requirements that 5V-only cards shouldn't be made anymore because
> this transition to 3.3V buses inevitably must happen, and you'd
> better not get caught out in the cold making 5V-only cards?  I'm
> glad the PCI SIG mandated this.

I still don't see "the mandate".  People can STILL design 5V only keyed
cards, apparently...and according to the 2.3 spec, they will work in the 2.3
compliant motherboards.  This is a good thing, IMO.  I also don't see why
the transition MUST happen...from a technological standpoint.  One could
argue it from a monetary standpoint though.

> I'm just surprised it didn't
> happen a lot sooner.

ISA has been around for 20 years, and people still want system boards with
an ISA slot.  MOST ISA stuff has been designed into the system board, but
there are still many ISA cards out there that people are using...

> Technology is the driving force.  But PCI plug-in cards haven't
> kept up with technology.

I don't believe it matters if PCI plug-in cards has or hasn't "kept up with
technology", because if the bandwidth of the PCI bus meets %99.999 of people
's uses, then what is the driving force for the change?  People's needs are
the driving force (as well as economics, which is a more valid point, IMO),
just like the inclusion of ISA into systems even into today.  There IS PCI
64/66, and there just aren't many cards out there for it, at least last time
I looked.  It has been VERY slow to catch on.

> They are slow and have gotten by with
> 1990 IC processing technologies.  Corelogic chipsets can't afford
> to do that.  So you're going to see 5V PCI buses disappearing
> from motherboards, not because the PCI Spec says so (it
> doesn't!), but because they just can't make them anymore.

Hum.  Why can't they make them anymore?  Does the technology to make them
simply disappear?  I don't think so.  I believe they CHOOSE to not make them
any more.  Certainly there are economics involved...but I'm not convinced
that economics are that strong, though I do know every penny counts in the
low end system board market...

> 5V-only PCI plug-in cards had better be scarce when that happens,
> or there will be a major technology disruption.

But what spec would they be complying to?

Again, thanks for the clarification and re-interpretation of the PCI 2.3
spec on 5V support on 2.3 compliant motherboards.  Obviously, the
interpretation that was posted previously to the list was incorrect, and 5V
plug-in cards are still supported.

Regards,

Austin