PLX lane splitters

[Art Vandelay]

To correct Linus, PLX chips do increase bandwidth, despite the increase in latency.

 

from Sin's review of the G1 Sniper 3

http://www.overclock.net/t/1262935/g1-sniper-3-review-plx8747vsnf200-circuit-analysis-ln2oc-core3d

 

 

PCIe 2.0 at X8 vs at X16 with a PLX

[Kuzma]

Oh wow O.o

[Emperor_Piehead]

Good job 3 way sli not. We need more lanes intel  and not lga 2011.

[Glenwing]

In a technical sense they do not increase bandwidth... But they can make available bandwidth that is not being used by other slots.

 

PLX chips function as a switch.  So instead of having for example 4 lanes to each of 4 slots, you can just put 16 lanes through a PLX chip and then to the four slots, and any of the four slots can use full 16 lanes bandwidth (just not all the slots can do so at the same time).  So this can give you additional bandwidth, because you put your dual slot graphics cards in every other slot with a few slots free, and lanes dedicated to them are unused, but if slots are wired to a PLX chip then instead of a graphics card slot being limited to 4 PCIe lanes or whatever, it can essentially "borrow" lanes from unused slots, because all the lanes are routed through the PLX chip and then distributed to the slots as needed.  Of course if you have a ton of PCIe cards that need high bandwidth, such as graphics cards, 10GbE network cards, RAID controllers, all in there together and you try to use them all at once at max bandwidth, the total number of lanes available to the system as a whole is still whatever is provided by the CPU or northbridge, not increased by a PLX chip.

[Art Vandelay]

In a technical sense they do not increase bandwidth... But they can make available bandwidth that is not being used by other slots.

 

PLX chips function as a switch.  So instead of having for example 4 lanes to each of 4 slots, you can just put 16 lanes through a PLX chip and then to the four slots, and any of the four slots can use full 16 lanes bandwidth (just not all the slots can do so at the same time).  So this can give you additional bandwidth, because you put your dual slot graphics cards in every other slot, if slots are wired to a PLX chip then instead of a graphics card slot being limited to 4 PCIe lanes or whatever, it can essentially "borrow" lanes from unused slots, because all the lanes are routed through the PLX chip and then distributed to the slots as needed.  Of course if you have a ton of PCIe cards that need high bandwidth, such as graphics cards, 10GbE network cards, RAID controllers, all in there together and you try to use them all at once at max bandwidth, the total number of lanes available to the system as a whole is still whatever is provided by the CPU or northbridge, not increased by a PLX chip.

That makes more sense. It still does improve performance, against Linus's claim that it's useless.