Precision Fixed Workstations

Last reply by 07-10-2021 Unsolved
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8656

Dell Precision T7500 PCI slots properties

I have a Dell T7500, and I'm trying to figure out what exactly I can do with it, and what I can put into it. 

I started looking for info about the PCI slots on the board and it's not so simple as there is even conflicting information in official T7500 documentation.

So I'm putting here everything I've found out for others to find, and also a few things that I'm still uncertain off:

- T7500 has 5 PCI slots.

- they are all full length x16 slots, but they don't all work as x16, they just have the physical dimensions of x16

They go as follows:

- PCI x8 Gen 2

- PCI x16 Gen 2 (x8 Gen2)

- PCI x8 Gen2

- PCI x16 Gen2 (x8 Gen2)

- PCI x4 Gen1

The chipset has only 32 PCI lanes so 2x16 or 4x8 lanes. The south bridge adds additional x4, that's why the x4 is Gen1 and has just 1GByte/sec speed. The other 4 slots work in pairs 8&16. If you utilize only the x16 slot, it works as x16, if you use the x8 slot, the x16 next to it drops to x8. This way we can have two full x16 Gen2 slots, or 4 x8 Gen2 slots in use - they always add up to 32 lanes. It's probable that the configuration 1x16 and 2x8 slots also works if we use just 3 slots (one of those x8 is obviously the slowed down x16 next to the first x8).

 

Now the info I'm missing is how much power can these slots supply?

The x4, it's pretty safe to bet that supplies a max of 25W.

The only info I have found is this:

Slot 2 PCI Express x16 with support for up to 300W,

Slot 4 PCI Express x16 with support for up to 225W, and then nothing about the x8 slots :(

What the **bleep** does that mean??? 300W???? The x16 slots should top out at 75W, the rest of the power comes from auxiliary power cables (6pin and 8pin). Why 300W? Two 8pins can work with 375W card, and there are cards with 2x8pin+1x6pin, which gives us 450W - why would the PCI slot care how many aux cables the card needs?

Also why does the second slot support only 225W? It's not powered at all, and all the power will come from the aux cables???

What about the x8 slots? I hope they supply also 75W, but if they supply only 25W it would be good to know :/

This is important since there isn't  a lot of physical space there so if you want to install two GPUs, each is 2slot (which seems to be slim these days, as now we have 3slot cards!!!!) and something else like a network card, you need to be creative with placing. I could place one of the cards in a x8 slot, it will work fine, maybe 3-5% slower than in x16, but if the x8 slot doesn't supply enough power, I risk frying the motherboard :/

So does anyone know how much power the PCI slots on this board deliver? Or has anyone mounted a GTX 1080 or 1080Ti in one of the x8 slots?

 

Replies (5)
4 Tellurium
8644

Hi @kaczorefx,

See if I could help answering your question.

1) Why would the PCI slot care how many aux cables the card needs?

The PCIe slot actually cares about how many current passing through as too much current may break the system. W(power) = A(current) x V(voltage). While voltage fixed at 12V for x16 slot, current would be the valuable for watt values. Therefore, "300w" means how many power accepted but not provided. Further reference on Wiki:

1.jpg

2) Also why does the second slot support only 225W?

I understand your feelings being confused.

Online support reference tells slot2 at 300w and slot4 at 225w

Technical Guide tells "It has two native Gen 2 PCIe x16 graphics slots each capable of driving graphics cards up to 225w".

Even worst, Spec sheet and Service Manual tells nothing about it...

Not sure why there's a difference here. But I guess, just a guess, it's the difference between max power support on a single slot and the whole system. Take my T5600 as example, there's a wordings in the T5600 Techincal Guidebook stating that "Total allowed graphics power allowed in slot 2 is 225W. Total graphics power allowed in system is 300W." Maybe it's the same case on T7500. Just maybe ^^"

3) What about the x8 slots? I hope they supply also 75W.

Yes, I understand again that all documents above say nothing about x8 slot. I also checked on the mainboard screenshot and same result:

2.jpg

However, this thread explained "All sizes of ×4 and ×8 PCI Express cards are allowed a maximum power consumption of 25 W." Therefore, sorry about it ^^"

4) Anyone mounted a GTX 1080 or 1080Ti in one of the x8 slots?

Take my T5600 experience as reference again. When I 1st install a RTX 2070 into slot4 of my system, it runs into Windows with no problem. But when I run GPU peak benchmark test, the system broke down and reboot immediately. Then, when I swap it to slot2, everything's fine again. Later I realize that slot4 of T5600 is actually "x16 (wired as x4)". Too much current detected by the PSU distribution board during GPU peak test and thus stop all power supply. Good job for the distribution board or my house would be burned!

Therefore, as mentioned above that x4 and x8 slots take the same limitation on power consumption, I'm afraid GTX 1080 or 1080Ti won't work on x8 slot. Better don't try.

“May the Force be with Dell.”
8631

Sh^%$^%ugar.

So that would mean I also can't install 1080ti or 2080ti in x16 slot4, which would be nice since a double slot card in it would overhang A PCI-x slot which is useless anyway.

But I can't do that because the cards are 250W - I have to mount them in slot2, which will cost me one of the x8 slots - who designs these boards?? It's a workstation and you can't even install two top cards in it!!!

Although the 2080ti has 2x8pin aux sockets, so at least it can get all of its power from them.

Your configuration probably bombed because 2070 is 175W and has only one 8pin, so this and your x4 25W PCI was exactly 175W - the test might have drawn a little more, so you were actually lacking on power, that's why PSU shut it down.

 

So now a new question, has anyone tried installing a 1080ti or 2080ti in slot4 in T7500?

8326

Why is slot 2 blue and slot 4 black? 

 

Dose 2 have a lower IRQ/FIQ? Did they run out of $COLOR plastic?

$signature>
8324

Interesting guess about short of plastic :BigSmile:

The blue color of a PCIe x16 slot stand for the default slot for GPU, and it used to be a common standard of motherboard. That means slot 2 default for GPU and slot 4 optional.

Due to card size and limited rooms within my T5600, I do have to install GPU on the optional slot.

“May the Force be with Dell.”
1873

05B2D256-498D-4EF7-BE98-4305710B044B.jpeg

And it work in that configuration 

T5600



 

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