Re: 3.3V / 5V PCI

[Quinn_Kunz@mtn.3com.com]

My responses are in <<..>> below in your text.




"William Benner" <william_benner@email.msn.com> on 09/02/98 06:21:23 PM

To:   Mailing List Recipients <pci-sig-request@znyx.com>
cc:    (Quinn Kunz/MTN/US/3Com)
Subject:  3.3V / 5V PCI




Hello All,

Several people have responded to my message regarding compatibility of 3.3V
and 5V connectors and peripheral boards. Those who have, unfortunately have
not followed my recommendation to post the response to this list and
instead
have replied directly to me.

In any event, so far the respondents have misunderstood the spirit of my
question. Understand that my question about placing a 5V PCI peripheral
board in a 3.3V PCI socket is mainly concerning the "signaling
environment",
NOT the power availability.

Again, the main questions are:

1) Are the latest motherboards coming out with ONLY 3.3V PCI connectors, or
do they still have 5V PCI connectors?

<<I'm not involved with motherboard design, however I have been looking for
motherboards that support a 3.3V PCI peripheral and so far there are no
commercial products available with 3.3V PCI keyed slots.  There are several
PC's that use chipsets that have 3.3V outputs and 5V tolerant inputs and
use 5V keyed PCI slots. For my personal testing purposes of 3.3V PCI, I can
accomplish the task by using a universal keyed board in these types of
systems.>>

2) If the latest motherboards still have 5V PCI connectors, how long will
it
be before we see 3.3V ONLY PCI connectors?

<<Good question?? I don't quite know the answer to that one other than PCI
peripheral mfg.'s and motherboard mfg.'s will have to coordinate their
efforts to make the push towards 3.3V PCI.  Otherwise, you will have
motherboards that have a 3.3V PCI slot and no 3.3V PCI peripheral's for the
consumer or vice versa.>>

3) If a motherboard has ONLY 3.3V PCI connectors, what does that "do" to
the
plethora of existing PCI plug in peripheral boards? (I think I know the
answer to this question, but I am asking so that I can say I asked the
experts and report the information to the president of my firm.)

<<Obviously if the motherboard only had 3.3V PCI slots, the consumer would
be limited to using only 3.3V PCI peripherals, of which I don't know of any
existing products today.  A motherboard manufacturer would be wise to have
the majority of the PCI slots be 5V and have one or two 3.3V PCI slots
through the transition.  I work in the mobile arena so I'm designing laptop
internal PCI peripherals, where 3.3V makes a lot of sense based on power
consumption and the bus/power rail voltage that is much more prevalent on
chipsets.  For the desktop arena however, there has to be a compelling
reason to transition to 3.3V PCI and so far power has not been a large
concern.  Going forward Microsoft is pushing 'On Now' in all platforms
which sets standards for power consumption on peripherals and support of
the "D" power states (D0-D3).  This may cause a push towards 3.3V PCI to
achieve the power consumption requirements????  Pure speculation since I do
not participate in the desktop arena.>>

William Benner