now as some of you may know uh Intel's
p67 platform has only 16 PCI Express
Lanes available for graphics configurations well basically available
for your main two PCI E slots here I'm going to show you a board that doesn't
have stuff installed on it so you've only got 16 PCI ex press
lanes for this one and this one which means you can either do 16x and actually
I think you can make it run at 1X so it might be 17 PCI Express lames not the
point okay so it's either 16 X or 8X 8X
on these two now some Sandy Bridge boards p67 boards that is have a third
PCI Express 16x physical slot this isn't the only one but this is the ASUS
p67 uh p8 p67 Deluxe and this one does
have a third slot so because there's only 16 Lanes running off of the CPU
itself for those graphics card slots
where does this extra PCI e6x slot run off of well
the answer is that this is actually only a PCIe 4X
slot and it actually runs off of the
chipset so there is an inherent delay
now the chipset does get a fair bit of bandwidth to the CPU itself but that
PCIe slot is actually not tied directly to the CPU the way that the other ones
are so I had someone ask me a question
what if you're running something like this like an ocz Revo Drive X2 to 40 gig
I happen to have one handy is there a performance difference
between running it off of a PCIe slot that's running off the CPU versus
running it off a PCIe slot that's running off what is essentially in
archaic terms the South Bridge so this video is an attempt to answer that I'm
just going to be using Crystal disc Mark to keep things simple and so I'm running
five uh five times the entire test I'm
running it over a 4 gig span of the drive and here are my results running it
in the in theory faster PCIe slot and
now I'm going to run it in the other PCI slot and see what happens well it would
appear that I have my answer the sequential numbers are oddly enough uh
very very close for reads uh this is
running off of the chipset PCI E slot
and then the screenshot I have here on the left is running off of the CPU PCI
Express slot so the sequential reads are pretty much Within margin of error the
sequential rights look to be a little bit higher on the on the chipset PCI
Express slot for whatever reason and then moving down into the random reads
and wrs it looks like for reads we're pretty much within the margin of error
but then for random rights for whatever reason actually well random reads here
you know what overall random performance seems to be higher on the CPU PCI
Express versus on the chipset PCI
Express and that does seem to be like a noticeable overall trend um so yeah I'm
not sure why that would be maybe it's to do with the latencies involved although
storage latencies are usually
um what I should say is uh is is chipset
latencies are usually nothing compared to storage latencies uh so I I wouldn't
have thought that it would affect it that much but it looks like uh for
whatever reason the the uh the lower latency between the CPU and this PCI
Express slot versus the CPU to that chipset to that PCI Express slot seems
to give us slightly better performance in random reads both in a light workload
scenario as well as in a heavy workload scenario so thank you for checking out
this little Linus Tech tips video about
the revo Drive X2 on the PC 67 chipset
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