RE: 3.3V / 5V PCI Question

[Andrew Ingraham <Andrew.Ingraham@digital.com>]

William,

I have seen several of the "Universal" PCI adapter cards.  You can spot
them even in the thumbnail pictures in catalogs (such as the catalogs of
networking products I occasionally receive) because of the two notches
in the connector.  A very rough estimate would be about 50-50 between
Universal and 5V-only cards, from a glance through one of these
catalogs.

Because Universal PCI add-in cards haven't become quite as commonplace
as was hoped, which would have eased the transition to 3.3V PCI
connectors on motherboards, the proposed version 2.2 of the PCI Spec
will encourage all new PCI add-in cards to be Universal (or ultimately
3.3V-only).  It also will require 3.3V power on all motherboard PCI
connectors, which can make it easier to build Universal add-in cards (no
need for 3.3V regulators on the card).

I believe that in the relatively near future, chipset manufacturers
(which means mainly Intel) will find it too difficult, or impossible, to
design in 5V-compatibility in their PCI interface, and they will be
forced to suddenly switch to 3.3V PCI buses and connectors.  They have
been stretching things already by using IC processes optimized for lower
voltages, while maintaining compatibility with 5V PCI.  The limit is
being reached.

When this happens, and it will, users with Universal add-in cards are
all set.  Those with 5V-only add-in cards will not be able to migrate
these cards from their old PCs to the new boxes.  Add-in vendors who
haven't yet made the move from 5V-only to Universal PCI add-in cards,
will suddenly find their market drying up.

66MHz PCI is also seeing some activity lately.  66MHz PCI (i.e.,
anything faster than 33MHz) requires a 3.3V interface with 3.3V
connectors on the motherboard.

Regards,
Andy Ingraham