Wednesday, July 20th 2011

Intel Mulls Propagating PCI-Express 2.0 x2 Interface

PCI-Express x1 met its match with the recent flood of devices such as 2-port SATA 6 Gbps and USB 3.0 controller chips that maintain their tiny package sizes thanks to a single-lane PCI-Express bus connection. The single-lane connection is already saturated with these kinds of devices: SATA 6 Gbps is moot with 250 MB/s per direction bandwidth of PCI-E 1.1, and could face bottlenecks with 500 MB/s of PCI-E 2.0, it is a similar case with USB 3.0 controllers. Use of PCI-Expresss x4, the bigger PCI-E bus standard, is a bad option as it increases PCI-E data pins by four times (significantly impacting chip package sizes), while eating into the limited lane budget of today's desktop chipsets.

The next best thing is PCI-Express 2.0 x2. While 2-lane PCI-Express is hypothetically possible, it has never been implemented by motherboard manufactures, neither on client, nor enterprise platforms. PCI-Express' parent organisation PCI-SIG doesn't have a slot or port specification for PCI-E x2, either. Intel seems to be of the idea that PCI-Express 2.0 x2 will provide immediate relief to manufacturers of small-footprint devices such as inexpensive third-party USB 3.0 and SATA 6 Gbps controllers, it provides a total of 2 GB/s bandwidth, 1 GB/s per direction, which greatly alleviates bandwidth bottlenecks, while not significanly increasing chip pin-counts. PCI-Express 3.0 is still in its infancy, while implementing PCI-Express 2.0 x2 is the easier, short-term solution. It will cause minimal R&D overhead on manufacturers to implement it. PCI-E 2.0 x2 will fit nicely into the limited lane budget of today's desktop chipsets.
Source: VR-Zone
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29 Comments on Intel Mulls Propagating PCI-Express 2.0 x2 Interface

#26
Wile E
Power User
I honestly don't see a problem with this. We already have the hardware to do it on the mobo side. There's no harm in developing add-on cards that use x2. I don't understand why some of you are against it. It won't hurt anything.
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#27
FordGT90Concept
"I go fast!1!11!1!"
DanTheBanjomanWhat would be their arguments to be against it?
Technical support calls, lots of them. People shove a 2x card into a 4x slot and find out either it doesn't work or it isn't getting the bandwidth they expected.
Wile EI honestly don't see a problem with this. We already have the hardware to do it on the mobo side. There's no harm in developing add-on cards that use x2. I don't understand why some of you are against it. It won't hurt anything.
Most hardware isn't set up to handle it because it isn't in the PCI-SIG specifications. Even by the off chance that some motherboards are wired for 2x, that doesn't mean the BIOS are ready.

We are against it because there's a high likelihood that if you buy a 2x card, either the system BIOS is going to reject it or you're only going to end up with 1x performance. In both cases, it defeats the purpose (just buy a 4x card and a non-POS motherboard and be done with it).

It's pretty obvious PCI-SIG felt that increments smaller than 4x were unnecssary; there's no reason for that to change today. We're talking like 3/4 inch longer on the slot and 4 times the performance. The difference in size is moot because virtually all motherboards are designed for at least one 16x slot.

If they were getting rid of everything larger than 4x, for example, then I could see justification for a 2x card. That simply isn't going to happen though (at least not any time soon).
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#28
Deleted member 3
FordGT90ConceptTechnical support calls, lots of them. People shove a 2x card into a 4x slot and find out either it doesn't work or it isn't getting the bandwidth they expected.
And this does not exist with x1 cards in x4 slots or any other combination? How about x16 physical with x4 electric? I really don't see how this is a valid argument.
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#29
Wile E
Power User
FordGT90ConceptTechnical support calls, lots of them. People shove a 2x card into a 4x slot and find out either it doesn't work or it isn't getting the bandwidth they expected.


Most hardware isn't set up to handle it because it isn't in the PCI-SIG specifications. Even by the off chance that some motherboards are wired for 2x, that doesn't mean the BIOS are ready.

We are against it because there's a high likelihood that if you buy a 2x card, either the system BIOS is going to reject it or you're only going to end up with 1x performance. In both cases, it defeats the purpose (just buy a 4x card and a non-POS motherboard and be done with it).

It's pretty obvious PCI-SIG felt that increments smaller than 4x were unnecssary; there's no reason for that to change today. We're talking like 3/4 inch longer on the slot and 4 times the performance. The difference in size is moot because virtually all motherboards are designed for at least one 16x slot.

If they were getting rid of everything larger than 4x, for example, then I could see justification for a 2x card. That simply isn't going to happen though (at least not any time soon).
BIOS update will fix most problems. Using a 2x card still leaves you with 2 lanes to use elsewhere where they may be more needed.

Sorry, but you don't have a valid argument against. Adding a 2x specification will not harm anyone, but could help at least a fringe market. Nothing you have stated has suggested otherwise.
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