can someone explain to me PCIe?

[BlahBlahYouToo]

or point me to a site that has a good explanation?

here's my basic understanding, which may be wrong and need to be corrected.
PCI shared bandwidth which was being saturated so there was a need for peripherals to have their dedicated bandwidth to communicate with the system.
(is there anything else, like interrupts and whatnot?)

so PCIe was developed to remedy this.
some lanes have more bandwidth than others.
some chipsets allow for multiple x16 lanes for running dual gfx cards.

other than video cards, i really haven't seen much else running PCIe. a couple of sound cards here and there.

 

[masteryoda34]

Gigabit ethernet comes close to exceeding PCI bandwidth. RAID cards also are using PCI-E now.

 

[tcsenter]

How about the stickey at the top of this forum category?

http://forums.anandtech.com/me...id=29&threadid=2297612

 

[BlahBlahYouToo]

1)
if a mb has two PCIe 2.0 x16 slots and says 2 (x16/x8) like this mb, and i want to run two gfx cards that are PCIe 2.0 x16 in SLI, what happens?
will i not get the full bandwidth? does it run in x8/x8?
by the way, how can they state that it has TWO PCIe x16 and then right after that state it is x16 and x8?

2)
i guess this is a follow up Q to Q1.
if i put an x16 gfx card into an x8 slot, will it work?
or is this not even physically possible because of the length of an x8 slot?

3)
if a mb has one PCIe 2.0 x16 slot and four PCIe x1 slots, how many "lanes" does it have? 20?
do the number of lanes really matter? as long as my peripheral cards fit into the slots and meet the requirements (e.g. in this example, i have 1 x16 card and 4 x1 cards), that should be all that matters right?

 

[Aluvus]

Originally posted by: BlahBlahYouToo


1)
if a mb has two PCIe 2.0 x16 slots and says 2 (x16/x8) like this mb, and i want to run two gfx cards that are PCIe 2.0 x16 in SLI, what happens?
will i not get the full bandwidth? does it run in x8/x8?
by the way, how can they state that it has TWO PCIe x16 and then right after that state it is x16 and x8?

The slots are physically the right size for PCI-Express x16, but don't have a full complement of 32 lanes between them. For that particular board, it means that if both slots are used they will both drop down to 8 lanes each (Anandtech review). This is a very common approach, and while it's not perfect it does work well enough.

I should also point out that that particular board supports Crossfire but not SLI.

2)
i guess this is a follow up Q to Q1.
if i put an x16 gfx card into an x8 slot, will it work?
or is this not even physically possible because of the length of an x8 slot?

I am not aware of any boards that actually use a slot for x8 that is physically different from x16. Certainly on consumer boards, the expectation is that any x8 slots will be used for x16 cards (that is, video cards).

3)
if a mb has one PCIe 2.0 x16 slot and four PCIe x1 slots, how many "lanes" does it have? 20?

Yes, that would be 20 lanes.

do the number of lanes really matter? as long as my peripheral cards fit into the slots and meet the requirements (e.g. in this example, i have 1 x16 card and 4 x1 cards), that should be all that matters right?

There is no particular reason to care about the total number of lanes, in and of itself. There are cases where it does indirectly matter (for instance, the board you linked to above doesn't have enough lanes to service all of its slots at full speed, so it has to make some adjustments).

 

[BlahBlahYouToo]

thanks aluvus.