About dual PCIe x16 slots

  • Thread starter Man-wai Chang ToDie (33.6k)
  • Start date

M

Man-wai Chang ToDie (33.6k)

if I plugged in a 16x VGA card into one PCIe x16 and
a 1x card into the other PCIe x16 slot,

would both PCIe x16 slot be slowed down to 8x?

--
@[email protected] Might, Courage, Vision, SINCERITY.
/ v \ Simplicity is Beauty! May the Force and Farce be with you!
/( _ )\ (Xubuntu 8.04.1) Linux 2.6.26.5
^ ^ 18:01:01 up 16 days 2:51 4 users load average: 1.03 1.03 1.00
? ? (CSSA):
http://www.swd.gov.hk/tc/index/site_pubsvc/page_socsecu/sub_addressesa/
 
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P

Paul

Man-wai Chang ToDie (33.6k) said:
if I plugged in a 16x VGA card into one PCIe x16 and
a 1x card into the other PCIe x16 slot,

would both PCIe x16 slot be slowed down to 8x?

It depends. Some chipsets offer two full and independent
x16 slots. In that case, there would be no effect from
one on the other.

There are many compromises possible with the lesser
chipsets. In particular, there are some, where in
fact the slots cannot go faster than x8. Even though
the advertising material on the web site and in
the manual states the primary slot is x16. It would
seem nobody does the analysis, to see what they're actually
capable of.

One chipset offered "bifurcation", with an x16 interface
and an x8 interface. Internally, the device only has
a total of x16 lanes of bandwidth. For that one, if
a card is only plugged into the x16 slot, it runs at
x16. If you plug in two cards, then the chip is switched
to x8/x8 mode. (Effectively, this is roughly equivalent
to some of the first generation motherboards, that used
a paddlecard to change operating modes.)

So you really need to look at datasheets, or summary information
about lanes on the chipsets, to deduce what you're actually
getting.

Paul
 
M

Man-wai Chang ToDie (33.6k)

It depends. Some chipsets offer two full and independent
x16 slots. In that case, there would be no effect from
one on the other.
.,...
So you really need to look at datasheets, or summary information
about lanes on the chipsets, to deduce what you're actually
getting.

Thanks. That mean I should look for a specification that
*EXPLICITLY* explain this.

--
@[email protected] Might, Courage, Vision, SINCERITY.
/ v \ Simplicity is Beauty! May the Force and Farce be with you!
/( _ )\ (Xubuntu 8.04.1) Linux 2.6.26.5
^ ^ 19:00:02 up 16 days 3:50 3 users load average: 1.03 1.05 1.01
? ? (CSSA):
http://www.swd.gov.hk/tc/index/site_pubsvc/page_socsecu/sub_addressesa/
 
P

Paul

Man-wai Chang ToDie (33.6k) said:
Thanks. That mean I should look for a specification that
*EXPLICITLY* explain this.

Honesty is a thing in short supply. It is easier
to leave the customer guessing.

Paul
 
M

Man-wai Chang ToDie (33.6k)

Paul said:
Honesty is a thing in short supply. It is easier
to leave the customer guessing.

Paul

Horn... nesty... is such a lonely word...
everybody is so un... true... :)

--
@[email protected] Might, Courage, Vision, SINCERITY.
/ v \ Simplicity is Beauty! May the Force and Farce be with you!
/( _ )\ (Xubuntu 8.04.1) Linux 2.6.26.5
^ ^ 21:55:01 up 16 days 6:45 3 users load average: 1.15 1.15 1.07
? ? (CSSA):
http://www.swd.gov.hk/tc/index/site_pubsvc/page_socsecu/sub_addressesa/
 
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J

John Weiss

Man-wai Chang ToDie (33.6k) said:
if I plugged in a 16x VGA card into one PCIe x16 and
a 1x card into the other PCIe x16 slot,

would both PCIe x16 slot be slowed down to 8x?

Depends on the chipset. The X48 chipset supports 2 full 16x slots.
 
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