can a pci expres 16x card be used in a 8x slot?
There are two issues. There is the mechanical design
of the connector. I've seen connectors x16 in size,
x4, and x1.
http://en.wikipedia.org/wiki/Image:PCIExpress.jpg
The second issue, is "lane wiring". Lanes can be set
up as powers of two. So lane numbers available are
x1, x2, x4, x8, x16.
A x16 slot can be wired for x8. It means half the pins
don't do anything. You can connect a video card to
a slot that has only x8 lanes, and it will work.
(There are many SLI boards that use x8 wiring.)
At least, I haven't seen any references to a video
card that won't work with x8 lanes.
I don't know of an easy way to predict what lane
wiring plans that video cards will have trouble with.
I know some motherboard manuals come with lists of
compatible video cards, which is a way of admitting
there is a problem with their PCI Express video slot.
If you see a manual like that, stay away.
I don't think the standard intended all possible
lane wiring plans x1, x2, x4, x8, x16 to be used.
Since the standard costs money, it isn't possible for
me to comment on its contents or intent.
I think this is the table in the standard (quoted from a
Dell article). Notice that x2 slot wiring is not mentioned
as an option:
*******
Table 3. PCI Express Card Interoperability
PCI Express Implementation x1_Slot x4_Slot x8_Slot x16_Slot
x1 Card Required Required Required Required
x4 Card No Required Allowed Allowed
x8 Card No Allowed* Required Allowed
x16 Card No No No Required
*These implementations will have an x8 connector on a wired x4 slot.
This means that the slot will accept x8 cards, but run at x4 speeds.
*******
Paul
