PCI express 2.0

[braando]

Can anyone venture an opinion regarding the new PCI express 2.0 standard (with double the bandwidth of the current standard), and what it will mean to things like the latest SLI MOBO (680i) and video cards like G80? What I mean is, will there be a new round of hardware in a month or two that will make those things obsolete or at least outdated?

I'm on the fence about buying and building a 680i system, but don't want it to be obsolete by the time I finish it.

 

[Rike]

I've not heard of anything that can currently use all of the bandwidth of a 16x PCIe slot. IIRC, there's very little performance difference b/n 8x/8x SLI and 16x/16x SLI.

Buy what makes you happy now. Everything from now will be outdated by something in 3 years or less.

 

[CrazyHelloDeli]

I heard the earliest we might see PCI-E 2.0 is at the end of '07.

 

[hardwareking]

pic-e 2.0 is supposed to be backward compatable.
So any pci-e card u buy today will work on those baords.

 

[Ilikepiedoyou]

Originally posted by: Rike
I've not heard of anything that can currently use all of the bandwidth of a 16x PCIe slot.

Really? I saw this written on a mobo description. 2 x PCI Express x16 slot (SLI mode: x16, x16) 1 x PCI Express x16 slot(third SLI slot in x8 mode)

what does this mean, it seems to relate to what you said?

 

[Rike]

Extra slots don't mean that all of the bandwidth of of the first two slots is being used. It just means you can put more cards in.

For example, a board with 2 16xPCIe + 1 8xPCIe could possibly run 3 graphics card (depends on the board) which would be handy if you needed to run 6 monitors. But even if you did that, there's no way (right now) that those buses are saturated with data.

 

[Ilikepiedoyou]

so are you saying that if I were to use one 16x card in a 16x slot it would run at that speed, but when you add a second in the next 16x slot, it will often down grade the speed to 8x?

 

[Fallen Kell]

Originally posted by: Ilikepiedoyou
so are you saying that if I were to use one 16x card in a 16x slot it would run at that speed, but when you add a second in the next 16x slot, it will often down grade the speed to 8x?

No. What he is saying is that the cards themselves do not hit the limit of the 16x slot. Just like hard drives out there do not hit the 300 MBPS bandwidth of SATA II connections. Most video cards do not have the need to use all the available bandwidth the full 16x slots allow them to use. He proof of that was when using a card in an 8x PCI-E slot, there is little to no pwerformance hit compaired to a full 16x slot. If the cards were using the full 16x of bandwidth, then you would expect an almost 50% performance hit if you cut the bandwidth by 50%.

As to your question on "if I were to use one 16x card in a 16x slot it would run at that speed, but when you add a second in the next 16x slot, it will often down grade the speed to 8x?", that will depend on your motherboard. All motherboards have a limited number of total PCI-E lanes that can be in use at one time. The motherboard chipset determines that total number. Many chipset do not have 32+ lanes of PCI-E, and thus can not run 2 16x PCI-E slots at full bandwidth at the same time. But since the motherboard manufacturers know that the video cards that are currently available do not really need 16 lanes of PCI-E bandwidth, they decided to still install 2 or more physical 16x PCI-E slots on the board, but at the software/BIOS level they will limit the number of PCI-E lanes that each slot has available to it. This is much like placing a rev limiter on a car (i.e. it restricts how much the slot is allowed to do depending on what it is set to. It can be set to have no limit, and use the full 16x that it is capable of, or it can be limited to using 1x, 2x, 4x, 8x as well. Some even allow complete tuning of the limits in 1x increaments). Other boards have a hard limiter in place (i.e. you can not control them at all, even though it is a 16x physical slot, it has a hard limit of only 8x speed). The reasons some do this is because it is cheaper to just have a hard limit then having a software tunible limit.

 

[Ilikepiedoyou]

Thanks for that. How exactly does the interface between the pcie slots and the north and south bridge work? Can pcie slots share the lanes, between them and between bridges as long as there is more than n time 16 lanes where n is the number of slots? The reason I ask so much, is because I would prefer to spend a little extra now and get soemthing that will last me well into the future as oppsosed to having to upgrade in the short term.

 

[Ilikepiedoyou]

bump

 

[Rike]

Originally posted by: Rike
Buy what makes you happy now. Everything from now will be outdated by something in 3 years or less.

I hate to quote myself, but there it is. You can wait for PCIe 2.0. It will be new tech you can buy on a mobo about one year from now and it will be mature tech in about 2 years.

So, you can buy now or save your money and have fun waiting. :disgust:

 

[Peter]

Originally posted by: hardwareking
pic-e 2.0 is supposed to be backward compatable.
So any pci-e card u buy today will work on those baords.

Compatible.

Yes, the double-frequency mode of PCIE 2.0 is planned to be optional; existing cards shall be working in future slots.

Let's talk again when the 2.0 standard has been finalized to begin with.

 

[Centurin]

IMO, DDR3 is the more important technology to be watching.

 

[Ilikepiedoyou]

I'm assuming ddr3 won't be backwards compatible.

 

[xenolith]

Originally posted by: Ilikepiedoyou
I'm assuming ddr3 won't be backwards compatible.

That is a correct assumption.