Basic PCI-E question

[aerisod]

I know this is a pretty basic question and I apologize for being dumb and not knowing the answer. I'm considering putting together a new system and had a question about PCI-E.

The motherboard I'm looking at is the Abit IP35 Pro and the manual says that the board has 3 PCI-E slots: PCI-E X16 (X16 bandwidth), PCI-E X16 (X4 Bandwidth) and PCI-E X1. The video card I'm looking at is the XFX 8800GT (PVT88PYDD4), which has a PCI-E 2.0 interface.

My question is will this card work on this motherboard? Is PCI-E X16 something completely different than PCI-E 2.0?

Thanks for any help!

 

[vexingv]

pci-e x16 slots are used for video cards. pci-e 2.0 is a specification for said slot. (as analogy, think of usb1 and usb2; same port but different specifications offering different performance, but usb2 is still backward compatible). pci-e 2.0 cards are backward compatible and at this point the performance difference b/t 2.0 are negligible. iirc, the new p35 chipset boards are pci-e 2.0 spec, but i may be wrong. pci-e x1 are used for expansion cards though most cards these days still tend to be legacy pci.

 

[myocardia]

Originally posted by: vexingv
iirc, the new p35 chipset boards are pci-e 2.0 spec, but i may be wrong.

All P35 boards are PCI-E 1.1, which is 100% compatible with PCI-E 2.0. The only chipsets available right now that has PCI-E 2.0 slots is the Intel X38, and the ATI 770 & 790 chipsets.


aerison, welcome to anandtech. I think I understand what you're wanting to know, so I'm going to answer your question differently than vexingv. A 16x PCI-E slot is different than 16x PCI-E bandwidth. There are three different sizes of PCI-E slots. The smallest is the 1x, then the 4x is about twice as long, and the 16x is roughly twice as long as the 4x. Those slots are also electrically incompatible. You can use an 8x card in a 16x slot, but you can't use either a 4x or a 1x card in one.

Now, on to the bandwidth portion. A 16x slot that's running @ 16x bandwidth can carry 16x as much data as a 1x slot, and 4 times as much data as a 4x slot. The Abit IP35 Pro has two 16x (physical) PCI-E slots, but only one of them has 16x bandwidth. Anyway, like I said above, all motherboards with the P35 chipset have PCI-E 1.1 slots, and they are all 100% compatible with all PCI-E 2.0 video cards.

 

[Peter]

Not quite.

There's three criteria:

(1) Mechanical slot length. There's 1x, 4x, 8x, and 16x, named by the max number of data lanes that can be implemented on such a slot. Also, the "longer" the slot, the more power may the card draw from it.

(2) Actual wiring. Slots can have fewer data lanes than their mechanical length suggests.

(3) Data lane speed. PCIE 2.0 optionally (!) doubles the speed from 2.5 GHz to 5. Note that if it says "PCIE 2.0" on the box, then that doesn't necessarily imply doubled lane speed.

Now, compatibility issues from these.

(1) If the card fits, it'll work. Plugging a "short" card into a "long" slot is allowed and perfectly fine, while "long" cards don't even mechanically fit into "short" slots.

(2) Both sides of a PCIE link (the card and the chipset) are expected to negotiate the number of available data lanes. Thus, you'll always get the best available mode of operation - plug a 16x card into a slot that is mechanically 16x but has only 4 data lanes, and you'll get 4x. Plug a 1x card into a 16x slot, and you'll get 1x.

(3) Likewise, double-speed mode is also automatically negotiated. If available on both ends, it'll be used, else the faster end will fall back to the original 2.5GHz mode.

 

[aerisod]

Thanks for the help, guys. Sounds like the PCI-E 2.0 card will work on the Abit IP35 Pro, which has PCI-E 1.1 slots.

Thanks again!

 

[amabee]

I am new here and dont mean to hijack your thread, but I have a similar question. Is PCIE 2.0 backwards compatible on all PCIE boards? I have an Intel DG965RY motherboard.

Thanks!

 

[Peter]

Answer is two up.