Calculating max graphics card bandwidth?? (NOT PCIe bus bandwidth.) - Overclock.net

Slink · 01-13-09

Tirelessly searching the web for an answer has been disappointing. Please help!

I apologize if this has been answered already.

Is it some physical hardware standard on a motherboard that draws the line of difference between PCI-E v1.0 and v2.0? Or is there some firmware upgrade that will allow for the upgrade from PCI-E v1.0 to v2.0? Potentially a new BIOS revision?

I ask because I can "upgrade" my motherboard to support some AM2+ CPU models, even though my board was released as an AM2 socket. Seeing as how the aperture of the AM2+ socket is physically identical to the AM2 aperture, I thought the same might apply to PCI-E, thought it's doubtful. Would be so so great.

This nice article merely hints toward "maybe". That's no more useful than what I already know, though there are some nice article links posted.

SECOND QUESTION!! Is there anyway that I or someone else can calculate my maximum vid card bandwidth to see if I am hitting the PCI-E 1.0 ceiling? My card is an XFX GeForce 9800 GTX+.

SIDENOTE: An interesting benefit to my wonderful mobo: I have double 16x SLI capability, (32x effective SLI, supposedly) even if I am limited to PCI-E 1.0. (See my system below my sig.), Therefore, my MB will still have headroom for maximization of the PCI-E graphics bus via dual SLI! ... Theoretically...

Thank you for reading, OCN goers!!

MadCatMk2 · 01-13-09

v2 cards do work on v1 slots with no issues at all and there's no such thing as update for the matter as far as I know.

Slink · 01-13-09

I am currently using a v2.0 card in a v1.0 slot. I just want to know if anyone can give me a definitive "no" that a v1.0 PCI-E slot cannot be "upgraded" to v2.0 by flashing the BIOS (or such).

Thanks.

GSkillz · 01-13-09

the type of pci-e slot is not gonna change with a bios update, but you should have no problems running your device in that slot anyway!

Slink · 01-14-09

Thank you. Now, how can I figure out how much of my PCI-E bus bandwidth I am using?

blitz6804 · 01-16-09

PCI-E 1.0 x16 is the same bandwidth as PCI-E 2.0 x8. There is no way to convert a PCI-E 1.0 slot into a PCI-E 2.0 slot. With a 9800 GTX+, you should not be too close to the bandwidth barrier I would think. The easiest way to check is to compare someone with the identical CPU speed/RAM speed as you running their GPU on a 2.0 x16 and see how much faster, if at all, it is compared to yours at 1.0 x16. (There is, however, a way to convert 2.0 slots into 1.0 slots. On my 790FX for example, there is a setting to "disable Gen2 mode.")

Slink · 01-16-09

Quote:

Originally Posted by blitz6804

PCI-E 1.0 x16 is the same bandwidth as PCI-E 2.0 x8. There is no way to convert a PCI-E 1.0 slot into a PCI-E 2.0 slot.

Yep, I have that much. Thanks again. (As PCIe2 is 2x the rate of PCIe1, that makes sense.) Mind you, I have a full 32 lanes of PCIe 1.0 if I use my SLI.

Quote:

Originally Posted by blitz6804

With a 9800 GTX+, you should not be too close to the bandwidth barrier I would think. The easiest way to check is to compare someone with the identical CPU speed/RAM speed as you running their GPU on a 2.0 x16 and see how much faster, if at all, it is compared to yours at 1.0 x16.

Thanks. I kinda figured as much, but I was hoping to find some formula for max bandwidth capability of my card, given gRAM amount, gRAM speed, GPU speed, etc.

ALSO, Has ANYONE definitely hit the PCIe1 barrier and tried the same card on a PCIe2 for absolute confirmation? Any comments or assistance is welcome.

Anyone else maybe know something? Thanks all!

blitz6804 · 01-17-09

I KNOW that the HD 4870x2 and GTX 295 will be past that "barrier." I have heard rumors that the HD 4870 and GTX 280 are possibly over.

I know the formula for memory bandwidth, but that is of little help here. For the record, that is:

Effective Speed (MHz) x Memory Bus width (Bits) = Bandwidth (Mbps)

So, in case of my HD 3850:

1800 MHz x 256-bits = 460,800 Mbps = 57.6 GBps

In the case of your 9800 GTX+

2200 MHz x 256-bits = 563,200 MBps = 70.4 GBps

We know that the memory bandwidth has nothing to do with the graphics throughput however, as the PCI-E 16x (PCI-E 2.0 8x) architecture is 4 GBps.

Slink · 01-17-09

Right, the PCIe interface allows the graphics card to communicate with the RAM (and/or CPU) via the PCIe bus. Thanks for the card info! I'll do some more Google-ing.

In the meantime,
READ THE SIG, HOMIES.

Can anyone else help meh?

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Calculating max graphics card bandwidth?? (NOT PCIe bus bandwidth.)

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