[geeks] pci express x8 video card?

[Charles Shannon Hendrix]

Wed, 14 Feb 2007 @ 09:45 -0500, Francois Dion said:

> Yes, that is correct. Similarly, in current boards with dual x16,
> since there are not enough lanes and it drops to x8 in an SLI setup.
> The video cards then operate at x8 even tough it is an x16 slot.

There are quite a lot of boards now whose chipset has 40 lanes or more.

Wether it matters or not depends on the nature of your I/O.

If a lot of it is direct I/O (device to device, bypassing the CPU), then
you benefit from that bandwidth. I would imagine that SLI does at least
a little bit of that. I could see it doing a whole lot in some cases.

Good drivers will let a lot of I/O bypass the CPU as well.

Otherwise, a CPU sitting on HyperTransport (or Intel's equivalent) at
1GHz can only write at 4GB/sec, with is half the bandwidth of a PCIe 16
slot.

Aside: I wish it were easier to snoop system busses so you could see what the
CPU and busses were doing while various programs ran.

-- 
shannon           | Consulting wouldn't be what it is today without Microsoft 
                  | Windows.
                  |        -- Chris Pinkham