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PCI Express x16 slot compatibility for Non-Graphics Applications?
This is about PCI Express x16 slot compatibility...
Does anyone know if there are any limitations of the PCI Express x16 ports that are shipping on desktop motherboards? For example, I get a Motherboard that has an Intel 915 chipset that has: 1 - x16 PCIe slot 1 - x1 PCIe slot 2 - legacy 32-bit PCI slots The documentation for the Chipset and Motherboards say that the x16 slot is PCI-Express compliant. But it also always puts in the note, "Intended for Graphics." Is this just so that the mainstream will get the hint it replaced the AGP slot? Or does it mean: "You'll have a hard time plugging in other stuff into this port you weird Non-Gamer." If I get a SCSI raid controller that has a x4 PCI-Express card edge connector on it. In theory, I can plug it into the x16 slot that is intended for graphics, Right?? Because I am using the embedded video port (don't need fast 3D video) and all I care about is the speed from the disks to the CPU, will everything be ok software/BIOS wise? In other words one more time, is there any limitation of the PEG port or PCI Express Graphics Port (x16 PCIe) that prevents other devices from taking advantage of the bandwidth available? Thanks, Jeff |
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#3
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The only devices using 16 lanes are graphics, and some high-speed
cluster interconnects. Most devices are 4 or 8 lane. The slots are different sizes, and you are supposed to be able to put an option with a lower lane requirement into a bigger slot - that is, the 8 lane should be able to plug into a 16 lane slot. You can't go the other way around. In addition, slots are not supposed to be underfunded (i.e. a 16 lane slot that only has 8 lanes on it) - with a notable exception - 8 lane slots can be underfunded with 4 lanes, and I believe that 8 lane devices are supposed to deal with it. Now that is assuming that the manufacturer complied with the standard. wrote in message oups.com... This is about PCI Express x16 slot compatibility... Does anyone know if there are any limitations of the PCI Express x16 ports that are shipping on desktop motherboards? For example, I get a Motherboard that has an Intel 915 chipset that has: 1 - x16 PCIe slot 1 - x1 PCIe slot 2 - legacy 32-bit PCI slots The documentation for the Chipset and Motherboards say that the x16 slot is PCI-Express compliant. But it also always puts in the note, "Intended for Graphics." Is this just so that the mainstream will get the hint it replaced the AGP slot? Or does it mean: "You'll have a hard time plugging in other stuff into this port you weird Non-Gamer." If I get a SCSI raid controller that has a x4 PCI-Express card edge connector on it. In theory, I can plug it into the x16 slot that is intended for graphics, Right?? Because I am using the embedded video port (don't need fast 3D video) and all I care about is the speed from the disks to the CPU, will everything be ok software/BIOS wise? In other words one more time, is there any limitation of the PEG port or PCI Express Graphics Port (x16 PCIe) that prevents other devices from taking advantage of the bandwidth available? Thanks, Jeff |
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Does that mean that it will run at x4?
Some of the x16 slots *hint* at maybe running at x16 or x1 only, nothing in the middle, if you plugged in a x4 you'd only get x1 speeds. Does anyone have any experience with this? |
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On 21 Apr 2005 16:59:42 -0700, " wrote:
Does that mean that it will run at x4? Some of the x16 slots *hint* at maybe running at x16 or x1 only, nothing in the middle, if you plugged in a x4 you'd only get x1 speeds. Does anyone have any experience with this? A PCI Express link goes through a training sequence to establish the total number of lanes supported by both ends. So an x8 or x4 or x1 device plugged into a 16-lane slot will train to x8 or x4 or x1, respectively. And any PCI Express-compliant device should work in any slot it can physically be plugged into (the restriction means you can't expect a x16 graphics card to plug into a slot that uses a physically shorter connector (eg: most x1 and x4 slots)... /daytripper |
#6
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On 21 Apr 2005 12:52:49 -0700, "
wrote: This is about PCI Express x16 slot compatibility... Does anyone know if there are any limitations of the PCI Express x16 ports that are shipping on desktop motherboards? At least in theory, no. For example, I get a Motherboard that has an Intel 915 chipset that has: 1 - x16 PCIe slot 1 - x1 PCIe slot 2 - legacy 32-bit PCI slots The documentation for the Chipset and Motherboards say that the x16 slot is PCI-Express compliant. But it also always puts in the note, "Intended for Graphics." Is this just so that the mainstream will get the hint it replaced the AGP slot? Or does it mean: "You'll have a hard time plugging in other stuff into this port you weird Non-Gamer." A bit of both. The system is designed so that it SHOULD be able to use any compatible PCI-Express card in the PCI-E 16x slot. However there are VERY few (none that I know of) PCI-E 16x cards out there that aren't video cards. To go along with that, the motherboard companies (and to a lesser extent the chipset companies) probably don't do much in the way of testing other PCI-E cards in these slots. If I get a SCSI raid controller that has a x4 PCI-Express card edge connector on it. In theory, I can plug it into the x16 slot that is intended for graphics, Right?? In theory yes, that is correct. Because I am using the embedded video port (don't need fast 3D video) and all I care about is the speed from the disks to the CPU, will everything be ok software/BIOS wise? Now THAT brings up a bit of an interesting question that you might not have thought of. When you add a PCI-E 16x graphics card into ALL boards using the i915 or i925 chipsets, it will *DISABLE* the integrated video (no way around this). So, the interesting question is, does putting a non-video card into that same 16x PCI-E slot ALSO disable the integrated video? ie is it just the fact that there's a video card in there or do the integrated video and 16x PCI-E slot itself share some resources? I honestly haven't got a clue about this one, though digging through Intel's datasheets might shed some light on this matter. Another option might be to simply look for a board with a PCI-Express 4x slot. They do exist, though they are quite rare. Or maybe consider a board using an ATI chipset, as they do NOT disable the integrated graphics when plugging in a PCI-E 16x video card. ------------- Tony Hill hilla underscore 20 at yahoo dot ca |
#7
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This is about PCI Express x16 slot compatibility...
Does anyone know if there are any limitations of the PCI Express x16 ports that are shipping on desktop motherboards? At least in theory, no. Can't speak for the OP, but I have x8 Infiniband cards that I'd love to plug in. Because I had seen dire warnings about x16 intended for graphics only, I had assumed my x8 card would not work in that configuration. Problem is that many desktop motherboards support x16 and x1 or maybe x4, very few support x8. Maybe the SLI boards may be different. (I'd love x8 for graphics + x8 for Infiniband network) I was hoping for some dual core desktops with IB to replace more expensive server boards. Tom's hardware did some tests a while back with configuring x16 slots at x8, x4 etc. It might be a useful read. I think his system required some unreleased BIOS update to unlock other speeds on the x16 slot. It didn't give me hope that BIOSes would support what I wanted to do. Probably a chipset manufacturer restriction to protect their server chipsets? So I haven't seen anyone tell me that physically the slot is different, but two things are unknown: 1) Would plugging something into the x16 slot mean the motherboard insisted it was used for graphics (rather than continuing to use the onboard graphics or say a slower PCI adapter) 2) Would attempting to use the x16 for a slower device be prevented by BIOS incompatabilities. Paul |
#8
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Now THAT brings up a bit of an interesting question that you might not
have thought of. When you add a PCI-E 16x graphics card into ALL boards using the i915 or i925 chipsets, it will *DISABLE* the integrated video (no way around this). So, the interesting question is, does putting a non-video card into that same 16x PCI-E slot ALSO disable the integrated video? ie is it just the fact that there's a video card in there or do the integrated video and 16x PCI-E slot itself share some resources? I honestly haven't got a clue about this one, though digging through Intel's datasheets might shed some light on this matter. The BIOS on Dell boxes with these chip sets (Dell 4700 & 8400) gives one the choice of using the integrated graphics even with a graphics card in the x16 slot. Perhaps this would do what the original poster desired: enable the integrated graphics even with a card in the x16 slot. Note: I did not actually test this BIOS option. |
#9
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On Fri, 22 Apr 2005 07:41:48 +0100, "Paul"
wrote: Tom's hardware did some tests a while back with configuring x16 slots at x8, x4 etc. It might be a useful read. I think his system required some unreleased BIOS update to unlock other speeds on the x16 slot. It didn't give me hope that BIOSes would support what I wanted to do. Probably a chipset manufacturer restriction to protect their server chipsets? So I haven't seen anyone tell me that physically the slot is different, but two things are unknown: 1) Would plugging something into the x16 slot mean the motherboard insisted it was used for graphics (rather than continuing to use the onboard graphics or say a slower PCI adapter) There's no accounting for stupid bios implementations. A smart one would realize whether a plugged-in agent had a video rom or not, before doing something stoopid like disabling embedded video. 2) Would attempting to use the x16 for a slower device be prevented by BIOS incompatabilities. See above. /daytripper |
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