pcie x16 x8 x4x x2 x1 ????

c-note

Hello knowledgeable ones...

i'm getting slightly confused about pcie, as i attempt to learn more in preparation for building my own pc.
now i know a bit about computers, where stuff should go etc!:p
but no indepth knowlege of how the stuff technically works together!

i'm focusing on the expansion slots on a motherboard.
for eg a mobo with 2 pcie x16 slots 2xpcie x1 slots and 2 pci slots

can you tell me what the x16 and x1 refers to when talking about pcie?
does it refer to "lanes" and are lanes just physical connections to the cpu or some other pcie controller which then connects to the cpu?

and how many "lanes" can a system have
eg imagine a mobo with 4 pciex16 slots:
if they were all populated does that mean that they'd all work at pciex4?

or imagine a board with 1 pciex16 populated witha gfx card
and 4 x1 slots populated by different cards
does that mean that the gfx card operates at x12 with the other 4 devices taking up x1 or will the gfx card still operate at x16?!

what spawned theese questions is that i've read on another post that a gigabyte p55a board only runs the gfx card at x8 even in the x16 slot when it has usb3/sata3 enabled (is this because the usb sata takes up 8 of the pci lanes or wha?!)

i suppose what i'm asking is
do pc's have 16 pcie "lanes" which must be divided amongst all pcie devices? in which case if you want a device running at x16 all other pcie expansion slots have to be empty?

maybe someone can clear this up or come up with an analogy for me

thanks in advance!!

Spear

c-note wrote: »

Hello knowledgeable ones...

i'm getting slightly confused about pcie, as i attempt to learn more in preparation for building my own pc.
now i know a bit about computers, where stuff should go etc!:p
but no indepth knowlege of how the stuff technically works together!

i'm focusing on the expansion slots on a motherboard.
for eg a mobo with 2 pcie x16 slots 2xpcie x1 slots and 2 pci slots

can you tell me what the x16 and x1 refers to when talking about pcie?
does it refer to "lanes" and are lanes just physical connections to the cpu or some other pcie controller which then connects to the cpu?

and how many "lanes" can a system have
eg imagine a mobo with 4 pciex16 slots:
if they were all populated does that mean that they'd all work at pciex4?

or imagine a board with 1 pciex16 populated witha gfx card
and 4 x1 slots populated by different cards
does that mean that the gfx card operates at x12 with the other 4 devices taking up x1 or will the gfx card still operate at x16?!

what spawned theese questions is that i've read on another post that a gigabyte p55a board only runs the gfx card at x8 even in the x16 slot when it has usb3/sata3 enabled (is this because the usb sata takes up 8 of the pci lanes or wha?!)

i suppose what i'm asking is
do pc's have 16 pcie "lanes" which must be divided amongst all pcie devices? in which case if you want a device running at x16 all other pcie expansion slots have to be empty?

maybe someone can clear this up or come up with an analogy for me

thanks in advance!!

PCI-E bandwidth is broken down into discrete groups called lanes. So a x6 slot has 16 lanes worth of bandwidth available. To further complicate things however, there may be only so many lanes of bandwidth available in total on the motherboard, anywhere from 20 to 40 or so depending on the age and quality.

http://en.wikipedia.org/wiki/PCIE

c-note

ahh ok
so lets say a mobo had 20 pcie lanes
that means you could have 1 pciex16 device running at x16
and 4 pciex1 devices running at x1
or
2 x16 devices running at x8
2 x2 devices running at x2

and a mobo with 40 pice lanes could have
2 x16 devies running at x16
and 2 x4 devices running at x4??

are there other devices which use the pcie lanes apart from expansion slots?

Spear

c-note wrote: »

ahh ok
so lets say a mobo had 20 pcie lanes
that means you could have 1 pciex16 device running at x16
and 4 pciex1 devices running at x1
or
2 x16 devices running at x8
2 x2 devices running at x2

and a mobo with 40 pice lanes could have
2 x16 devies running at x16
and 2 x4 devices running at x4??

are there other devices which use the pcie lanes apart from expansion slots?

Most onboard devices will use a lane each as well. It depends a lot on the board design and whether integrated devices are discrete or not.

c-note

right, i'm getting the picutre.

i guesss thats why the gigabyte borad with the usb3&sata3 chip only runs the gfx card at x8 in a x16slot, because the usb3&sata3 is using some of the pcie lanes?
i suppose if you wanted sli you have to run both cards at x4!

Leman_Russ

c-note wrote: »

right, i'm getting the picutre.

i guesss thats why the gigabyte borad with the usb3&sata3 chip only runs the gfx card at x8 in a x16slot, because the usb3&sata3 is using some of the pcie lanes?
i suppose if you wanted sli you have to run both cards at x4!

Yes, you have to run the cards at x4.

However, if you have GOOD Graphics cards (aka ATI 58xx) The Performance Drop is only 5% http://www.techpowerup.com/reviews/AMD/HD_5870_PCI-Express_Scaling/1.html

c-note

Excellent i think i have a handle on it now,

the gigabyte manuals do have a useful block diagram showing what devices use what buses (the usb3 and sata3 on the gb p55a ud4 are indeed on the pcie bus and use up pcie lanes)

final question:
how can you tell how many pcie lanes a motherboard has.
i have looked through the manuals of
gigabyte p55 ud4
gigabyte p55a ud4
intel dp55wg
and havnt found any info on pcie lanes (or does the number of lanes depend on the chipset,p55?)

edit
final final question
lets say i have a gfx card in a x16 slot running at x16
could adding (for arguements sake) a soundcard in the x8 slot, reduce the bandwidth for the gfx card?

Leman_Russ

c-note wrote: »

(or does the number of lanes depend on the chipset,p55?)

Ding ding ding