PCIe x16 2.0

[Man-wai Chang ToDie]

Does current generation of PCIe VGA card work at maximum speed in a
motherboard that supports PCIe 2.0?

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[Paul]

Does current generation of PCIe VGA card work at maximum speed in a
motherboard that supports PCIe 2.0?

As far as I know, there are four possible combinations.

PCI Express 1.0 motherboard + PCI Express 1.0 video card = existing, works good

PCI Express 2.0 motherboard + PCI Express 1.0 video card = no complaints reported
PCI Express 2.0 motherboard + PCI Express 2.0 video card = haven't seen a review,
no idea if it helps a lot

PCI Express 1.0 motherboard + PCI Express 2.0 video card = ...
Problem with VIA chipset motherboards. If the card is an
8800GT, you may profit from flashing the video card BIOS
to a PCI Express 1.0 BIOS specifically for the card.
Apparently, auto-negotiation can be disabled on the
video card, and that will help the card work with a
VIA chipset board.

The PCI Express 2.0 standard is meant to offer additional
bandwidth over the existing 4GB/sec bidirectional that
the existing standard provided. You can review the benchmarks
here, to see the effect that slot bandwidth has on video
card performance. Look at more than just this one page, as
one of the other benchmarks is more sensitive to bandwidth.

http://www.tomshardware.com/2004/11/22/sli_is_coming/page10.html

Paul

 

[Man-wai Chang ToDie]

PCI Express 2.0 motherboard + PCI Express 1.0 video card = no complaints

reported
The PCI Express 2.0 standard is meant to offer additional
bandwidth over the existing 4GB/sec bidirectional that

Do I need a VGA card that has explicit support for PCIe 2.0 in order to
get that 4GBps bandwidth (sort of like SATA I vs II)?

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[Paul]

Do I need a VGA card that has explicit support for PCIe 2.0 in order to
get that 4GBps bandwidth (sort of like SATA I vs II)?

A PCI Express 1.0 video card, gets 4GB/sec on each of the
two busses. There is a transmit bus and a receive bus.
They can operate simultaneously. (4GB/sec = 16 x 250MB/sec,
and is based on x16 lanes)

If a PCI Express 2.0 video card is paired with a PCI Express 2.0
motherboard (x38 motherboard, 8800GT video card), then the
numbers change to 8GB/sec transmit and 8GB/sec receive.
(8GB/sec = 16 x 500MB/sec)

If a PCI Express 2.0 video card is operated with a PCI
Express 1.0 motherboard, then the communications would remain
at 4GB/sec.

So in a way, it is exactly like SATA, in that autonegotiation
works most of the time, and the speed will be 4GB/sec or
8GB/sec, depending on what both ends are capable of.

Paul

 

[Man-wai Chang ToDie]

If a PCI Express 2.0 video card is paired with a PCI Express 2.0

motherboard (x38 motherboard, 8800GT video card), then the
numbers change to 8GB/sec transmit and 8GB/sec receive.
(8GB/sec = 16 x 500MB/sec)

Thanks. So a video card must declare itself to be PCIe 2.0 if they wanna
be sold at higher prices?

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[Paul]

Thanks. So a video card must declare itself to be PCIe 2.0 if they wanna
be sold at higher prices?

PCI Express 2.0 operation is not being heavily promoted. It is
almost an invisible feature right now. I'm sure if I asked
ten people about their new video card, nine of them would not know
it was capable of PCI Express 2.0 operation. So I don't see
them making much money off the feature.

A lot of people right now, cannot think of a good reason to
buy an X38 based motherboard. X38 has PCI Express 2.0 and
it also has ECC. But most people only care about
overclocking.

Paul

 

[Man-wai Chang ToDie]

PCI Express 2.0 operation is not being heavily promoted. It is

A lot of people right now, cannot think of a good reason to
buy an X38 based motherboard. X38 has PCI Express 2.0 and
it also has ECC. But most people only care about
overclocking.

Would it end up like the change from AGP 4x to 8x, which has little
improvement after all?

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[Paul]

Would it end up like the change from AGP 4x to 8x, which has little
improvement after all?

In some situations that would be true. The Tomshardware benchmarks show
how bandwidth dependent some games are. The percentage improvement
may not be sufficient, to justify purchasing yet another motherboard
just for PCI Express 2.0 slots.

Paul

 

[DaveW]

Yes, the card runs at its rated speed.

 

[Man-wai Chang ToDie]

Thanks to all!

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