Can someone explain the PCI variations to me?

[vlack]

PCI-X <- Apple ships G5s with these, and the Dell server boards are with these too?
64bit/66MHz PCI
32bit/33MHz PCI <- "normal" PCI, right?
And then one or two in between... 32bit/66MHz or something like that, I think.

And then there's PCI-Express coming out soon.

What's with the notches in strange places (on the physical bus)?
"normal" PCI has them like
|||||||||||||||||| |||

, but the one non-PCI-X slots in my Dell server looks like this:
||| ||||||||||||||||||

while some cards come with notches in both places:
||| |||||||||||||| |||

And then of course physically longer busses have different slots... I'm very confused...

This is all for gathering information on which server board to buy. My initial concern was that I might want to upgrade to a 3ware ATA RAID card sometime in the future (upgrade from linux software RAID), and 3ware.com says that they require 64bit/66MHz PCI slots for all their newer cards. So I went looking for boards that support that, and they seem to be very few and far between - most boards seem to have PCI-X slots only.

This board:
http://www.tyan.com/products/html/thunderk8w.html

Is PCI-X just a name for something that's not PCI 32bit/33MHz? So there are PCI-X slots up to 64bit/133MHz, and to make a 3ware card work I only need the older PCI-X specification of 64bit/66MHz?

Or am I totally off?

And finally: if the specifications are all different, which one should I try to get so that I can ensure that several years down the line I'll actually still have products to buy for my PCI-abcdefg slot?

 

[Peter]

The key tab is for the slot voltage. "Normal" PCI as you call it is 5V, while all the faster variants are 3.3V. Cards have a matching notch for voltages they're compatible with. As you noticed already, there are universal cards that run in 3.3V or 5V slots.

64-bit slots are longer, of course.

PCI-X slots are 64-bit 3.3V and 133, 100, or 66 MHz, depending on how many cards are on the same bus. And they're backwards compatible to plain PCI at 66 or 33 MHz.

If you plug a slow-clock card into a fast slot, that'll work, but kick the entire bus segment back to that slow speed. E.g. if you plug a (3.3V compatible) 33 MHz PCI card into a PCI-X 133 MHz slot, you'll get 33 MHz.

That 3ware card would be doing OK in a PCI-X slot, you'd just get 66 MHz PCI not the more efficient PCI-X. So you want to plug it into a slot that does not share the bus segment with an onboard PCI-X device. (K8W gives you two PCI-X bus segments to plug stuff into, see product page.)