PCIe x16 Slot Compatibility

[wrems]

Can one stick any PCIe x1, x4, x8 card into an available x16 slot?

[PLUCKYHD]

Originally Posted by wrems

Can one stick any PCIe x1, x4, x8 card into an available x16 slot?

That is my understanding unless it is dedicated to graphics only (some motherboards do this). But I believe pci express is downgradable just not upgradable (ie a 1x can go in a 4x but not the other way around)

[PiX64]

Take a look at the wikipedia page...some good stuff on there that will def. answer your questions...quite a bit more info than most people care about, but your answer is there nonetheless...


http://en.wikipedia.org/wiki/PCI_Express

[wrems]

Originally Posted by PiX64

Take a look at the wikipedia page...some good stuff on there that will def. answer your questions...quite a bit more info than most people care about, but your answer is there nonetheless...


http://en.wikipedia.org/wiki/PCI_Express

I read (skimmed) that wikipedia page and didn't find my answer. I just re-read it and found the info I was looking for. I too had Plucky's understanding and wanted to knwo for sure.

Thanks!

[PiX64]

AWESOME!. I was pretty sure plucky was right was well, but had to read through the entire wiki page cause well...im kinda a nerd like that :-)

[paulbeers]

And to sum up. YES YOU CAN. Heck you can even run a graphics card off of a 1X slot (if the slot has an "open end"), but you will just be limiting the data bandwidth (i.e. slowing the card down). It is honestly one of the best parts about PCIE is how interchangeable everything is (oh and the extra bandwidth is nice as well ). Heck, I ran my Hauppauge HVR2250 in my 16x slot for awhile.

[Taddeusz]

Yea, it's actually a recommendation by the PCI-SIG that all slots be physically x16 no matter how many lanes each slot has, like on the Mac Pro motherboard. That way any card can go in any slot and it's just a matter of bandwidth available to each one.

I saw a picture of a new board, coming out from Giga-byte I think, that has all x16 slots. No explanation of how much bandwidth each slot gets though.

I'm sure that consumer boards will continue to have a single x16 slot for video and x1 slots for other peripherals while workstation and server boards will likely be populated by all x16 slots.

[davephan]

I am using a HVR-2250 PCI-e X1 in a X16 slot.

Dave

[drewg]

Originally Posted by Taddeusz

Yea, it's actually a recommendation by the PCI-SIG that all slots be physically x16 no matter how many lanes each slot has, like on the Mac Pro motherboard. That way any card can go in any slot and it's just a matter of bandwidth available to each one.

In most cases, that's massively stupid, because users will end up putting the card in the wrong slot. Eg, you'll put your x16 Gen2 graphics card in a slot that's x16 physical, but x1 electrical, and put your x1 TV tuner in the x16 slot, and then wonder why performance sucks. I work for a 10GbE NIC vendor, and that happens to us every day. One of the first things our diagnostics (and driver) do is to check the number of lanes our card got, and warn the user if it is less than 8 (its an x8 10GbE NIC).

The one machine I've ever seen that actually took advantage of the flexibility that making all slots x16 provided was the first generation Mac Pro. It has a wiz-bang gui that lets you re-allocate bandwidth between slots, and will warn you if you have a card in a slot that is getting less bandwidth than it should. They stopped doing that in later Mac Pros, I guess it was either too expensive, or maybe the Intel 5400 and 55x0 chipsets didn't support re-assigning bandwidth like the 5000 did.

Drew

[Savage1701]

Might as well throw my 2-cents worth in - Yes, you should be able to. On most consumer and enthusiast boards they want you to put your graphics card in a certain slot and boot it first so it grabs all 16 lanes. But, then again, some enthusiast boards allow you to control how many electrical lanes each slot, or at least some of the slots, receive in BIOS, so if you have a double width card you could make sure it got plenty of lanes by grabbing some from an adjacent blocked slot.

Some boards will also allow you to pull jumpers next to each express slot to electrically disable it to allow you lattitude in trouble shooting. That's a nice feature as well.

If you look at some of the high-end SuperMicro server boards they are all physical x16 with a combo of electrical 2.0 x16 and/or x8.

Just remember, even a puny x1 version 1.0 lane gives you about 200-250 megabytes per second after overhead and assuming your x1 device can keep up.

Also, it's sort of rare to see x1 slots with open ends on them that you can actually drop a physical x16 card into.

I agree with the above poster - all slots ought to be physical x16 no matter how many electrical lanes (1,4,8 or 16) they offer, especially since most motherboard vendors don't offer open-end x1 slots.

[MattHelm]

Originally Posted by Savage1701

I agree with the above poster - all slots ought to be physical x16 no matter how many electrical lanes (1,4,8 or 16) they offer, especially since most motherboard vendors don't offer open-end x1 slots.

The problem with that, is a x16 physical slot must supply the POWER connectors for a x16 slot. This is 16x the power requirements of a x1 slot. You MB spec will REQUIRE a larger power supply. An open ended x1 slot only requires power for a x1 slot. That's my guess for only having x1/x4 slots, and not all x16 slots.

(the early pce-e scaling test made sure they only covered the signal pins, not the power pins on the x16 slots)

[Taddeusz]

Originally Posted by MattHelm

The problem with that, is a x16 physical slot must supply the POWER connectors for a x16 slot. This is 16x the power requirements of a x1 slot. You MB spec will REQUIRE a larger power supply. An open ended x1 slot only requires power for a x1 slot. That's my guess for only having x1/x4 slots, and not all x16 slots.

(the early pce-e scaling test made sure they only covered the signal pins, not the power pins on the x16 slots)

Not really, the power to the slot is on the pins prior to the notch. Everything after that are the data lanes. The motherboard will supply as much power as needed as long as it doesn't fall outside the power specification for PCIe and then it will need external power like video cards. The number of lanes has no affect on how much power is provided.

[paulbeers]

Originally Posted by Taddeusz

Not really, the power to the slot is on the pins prior to the notch. Everything after that are the data lanes. The motherboard will supply as much power as needed as long as it doesn't fall outside the power specification for PCIe and then it will need external power like video cards. The number of lanes has no affect on how much power is provided.

Just to show Taddeusz is correct:

http://en.wikipedia.org/wiki/PCI-E#Pinout

All power pins are in the first "section" before the notch...

This all reminds me of my old Dell PowerEdge SC420. It had a single PCIE 8x slot (and only sized for an 8X slot since it was actually considerd a server due to some dividers). By taking a dremel/Xacto Knife/etc, you could cut the back dividers of the PCIE slot and drop in any 16X video card and have a heck of a gaming rig for almost nothing (I think I got mine for $250?).