On Fri, 2005-06-17 at 05:47 -0700, [EMAIL PROTECTED] wrote:
> I have a Tyan K8S-Pro (2882) which has 1 PCI slot and 4 open slots on
> two PCI-X buses. It also has a crummy graphics chip which I want to
> replace with a PCI card I have. but that single PCI slot is occupied
> by a USB/Firewire board. I have a different USB/Firewire PCI board
> which may or may not be PCI-X; the store said yes, the box and manual
> say nothing. A web search didn't turn up much else.
>
> Does anyone know if PCI cards can be put in PCI-X slots? I would not
> mind if that PCI-X bus then slowed down to the lowest common speed.
> This motherboard has two PCI-X buses, and I don't mind filling one
> with PCI cards if that is possible. The FAQs I found were not exactly
> enlightening. They seemed to want to give the impression that PCI and
> PCI-X were compatible design-wise, without actually saying anything
> practical to users, such as Can I Stuff A PCI Card Into A PCI-X Slot?
From what I've read and been told, PCI X is simply an electrical
extension cord for PCI. The voltages, speeds, and number of signal
wires of PCI differ with the revision and I think that is the same with
PCI X but because of the low voltages and high signal rates the
wires/interconnects can't be very long and the number of things that can
plug into the bus can't be very many because each new connector (used or
not) introduces more noise onto the bus. That noise can't exceed a
certain threshold or the signals become corrupt. The way around this
issue is PCI X where a PCI X gives you a couple more slots a little
further away from the main PCI slot and simply reads the data from the
devices on the PCI X bus and writes it to the PCI bus. The act of
reading and writing cleans out all of the noise from the PCI X bus and
amplifies the PCI signal back up to the standard voltage for the PCI
bus. The higher the voltage the further the signal will travel but the
more it will bleed into the neighboring lines (PCI is a parallel bus
arch). The lower the voltage the less bleeding (also called crosstalk)
and the more times the data can change (from 0 to 1) leading to a faster
data rate. I'm not an Electrical Engineer but a friend of mine is and
that is the way that he explained it to me. So PCI X should just be an
extension to PCI but it could also be possible to change the data rate
and voltage by adding a buffer so that the extension talks at one rate
and voltage on one side and a different rate and voltage on the other.
That is where checking the documentation for your particular
implementation comes in. Some PCI controllers can handle changing
voltages and data rates to talk to older/newer (faster or slower) cards
and some can't. Not all controllers are backwards compatible and
therefore can't handle the higher voltages and slower signal rates of
older cards.
This should not be confused with PCI E where the E does something
similar to the difference between PATA and SATA. By using less wires
(by going serial) the cross talk is minimized and the data rate can be
turned up a lot higher. So for instance a nVidia 6800E has four PCI E
channels so there are four separate serial communication links between
the card and the controller instead of the 32/64 that PCI would have but
each one is going a lot faster and that makes up for the difference in
the number of wires.
I hope that clarifies more than confuses,
--
Tres
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