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PCIe vs PCIX vs PCIe x1 vs PCIe x16

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PCIe vs PCIX vs PCIe x1 vs PCIe x16

Postby OneWorld » Sat Nov 24, 2012 1:06 pm

Although I thought I had 'got it' I am still confused by the PCI Express thing. I thought PCIe was superceding PCIX. But I have 2 PCIe x 1 slots (the very short stumpy connector) on my motherboard, 3 ordinary PCI slots and one which is physically about the same length as the ordinary PCI slot but it shown as a PCIe x16 in the motherboard manual, but it looks suspicioulsy like a PCIX.

Well if PCIe is superceding PCIX, how come it says in the motherboard manual the PCIe slots are x1 and the longer PCIe x16 is faster? Or I would have thought so seeing as it says "x 16"
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Re: PCIe vs PCIX vs PCIe x1 vs PCIe x16

Postby Karl H. » Sat Nov 24, 2012 5:32 pm

As far as I have understood things, PCIX was a pretty straight-forward extension of PCI (possibility of 64-bits wide rather than 32 bit, doubled clock rate from 33 MHz to 66 MHz).

However, it looks like this was too small a step for most industry players, so PCIe appeared, which is a serial bus (unlike PCI and PCIX). Instead of having 32 or 64 parallel lines at relatively low clock rates, they choose to go with serial (1 bit wide) at much higher clock rate. This is a general trend in the industry, same thing with SATA, for example.

PCIe x1 means just one serial channel, while PICe x16 has 16 serial channels, and should therefore have 16 times the throughput. The reason this still works better than parallel is that in 16x, each serial channel has its own clock, so skew is not a problem like it was in the parallel configuration (when all the data lines shared a single clock).
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Re: PCIe vs PCIX vs PCIe x1 vs PCIe x16

Postby OneWorld » Sat Nov 24, 2012 7:34 pm

Karl H. wrote:As far as I have understood things, PCIX was a pretty straight-forward extension of PCI (possibility of 64-bits wide rather than 32 bit, doubled clock rate from 33 MHz to 66 MHz).

However, it looks like this was too small a step for most industry players, so PCIe appeared, which is a serial bus (unlike PCI and PCIX). Instead of having 32 or 64 parallel lines at relatively low clock rates, they choose to go with serial (1 bit wide) at much higher clock rate. This is a general trend in the industry, same thing with SATA, for example.

PCIe x1 means just one serial channel, while PICe x16 has 16 serial channels, and should therefore have 16 times the throughput. The reason this still works better than parallel is that in 16x, each serial channel has its own clock, so skew is not a problem like it was in the parallel configuration (when all the data lines shared a single clock).

Thanks,

So, the PCIE x 16 and a PCIX slot are definitely 2 different things. I can see the PCIe x 1 looks radically different - it is a very small connector. But the PCIe x 16 looks like an ordinary PCI slot, which in turn looks like PCIX.

Am I right in thinking that an ordinary PCI card will fit in a PCIE x 16 slot?
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Re: PCIe vs PCIX vs PCIe x1 vs PCIe x16

Postby DGL. » Sat Nov 24, 2012 7:47 pm

No it won't. All PCI Express cards will fit in the bigger X16 socket (but not the other way round) but not standard PCI cards.
A PCI and PCIe X16 slot is actually keyed differently and anyway there are two different communication methods involved here (parallel vs. serial).
Only standard PCI cards will fit in pci slots (both PCIX and PCI) and only PCI Express cards will fit in PCI Express sockets.
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Re: PCIe vs PCIX vs PCIe x1 vs PCIe x16

Postby Karl H. » Sat Nov 24, 2012 10:39 pm

OneWorld wrote:

Thanks,

So, the PCIE x 16 and a PCIX slot are definitely 2 different things. I can see the PCIe x 1 looks radically different - it is a very small connector. But the PCIe x 16 looks like an ordinary PCI slot, which in turn looks like PCIX.

Am I right in thinking that an ordinary PCI card will fit in a PCIE x 16 slot?

No. PCI (and PCI-X) is parallel, and PCIe is serial, so they are fundamentally incompatible.

Maybe it's non-intuitive, but a PCIe x1 card will actually work in a PCIe x16 slot...
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Re: PCIe vs PCIX vs PCIe x1 vs PCIe x16

Postby OneWorld » Sun Nov 25, 2012 11:50 am

Thanks everyone, I got it now, I was under the impression that PCIE x16 and PCIX were one and the same thing as sometimes I have heard of both PCIe and PCIX referred to as PCI Express
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Re: PCIe vs PCIX vs PCIe x1 vs PCIe x16

Postby Pete Kaine » Mon Nov 26, 2012 11:09 am

DGL. wrote:All PCI Express cards will fit in the bigger X16 socket (but not the other way round)

You've clearly never taken a hack saw to a PCIe gfx card
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Re: PCIe vs PCIX vs PCIe x1 vs PCIe x16

Postby zenguitar » Mon Nov 26, 2012 12:43 pm

Pete Kaine wrote:

You've clearly never taken a hack saw to a PCIe gfx card

Use a Dremel with a disc cutter Pete. Looks FAR more impressive, especially if the customer is watching you work

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Re: PCIe vs PCIX vs PCIe x1 vs PCIe x16

Postby Pete Kaine » Tue Nov 27, 2012 9:45 am

Thats true!

Far more precise too.
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Re: PCIe vs PCIX vs PCIe x1 vs PCIe x16

Postby zenguitar » Tue Nov 27, 2012 12:47 pm

When I had a guitar workshop in a shop unit I used to have loads of fun with that. If a client bought in a Strat and I was free to start straight away I would start chatting to keep them in the shop for a few minutes.

As I talked I would start dismantling the guitar. Slacken the strings, grab them all together and pick up a MASSIVE cutter and snip all 6 strings at once. That always got the first flinch. Remove the remnants of the strings, then I would grab the cordless screwdriver and start removing screws. Neck off first, then the trem, then the scratch plate and electrics... all the time keeping up a conversation with the customer. Then I would reduce the trem to a pile of parts.

The look on their faces as you casually reduced their pride and joy into a pile of bits in less than 5 minutes whilst chatting and hardly glancing at the guitar as you did it. Priceless

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Re: PCIe vs PCIX vs PCIe x1 vs PCIe x16

Postby Goddard » Tue Nov 27, 2012 3:19 pm

Not clear why one would need to hack at a PCIe gfx card. To fit into a shorter slot?

If that, then perhaps easier to simply melt down the back end of the slot connector to open it out. Some x1, x4 and z8 slot connectors actually come open-ended to accept longer card edge connectors.

Now, hacking away at the edge connectors on PCI-X cards still seems to be popular with old PCI-X ProFools DSP cards, to fit them into regular PCI slots while allowing the overhanging bit to clear motherboard components (the PCI-X extended bit was just nonfunctional marketing cosmetics done by Digi after Apple dropped PCI slots in favor of PCI-X).
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Re: PCIe vs PCIX vs PCIe x1 vs PCIe x16

Postby Pete Kaine » Wed Nov 28, 2012 11:10 am

zenguitar wrote:When I had a guitar workshop in a shop unit I used to have loads of fun with that. If a client bought in a Strat and I was free to start straight away I would start chatting to keep them in the shop for a few minutes.

I suppose it would appear quite scary to witness to anyone who hands over a tresured possession to someone doing work on it if they don't know their way around it to the same degree.

Slightly evil, but good fun!


Goddard wrote:Not clear why one would need to hack at a PCIe gfx card. To fit into a shorter slot?

If that, then perhaps easier to simply melt down the back end of the slot connector to open it out. Some x1, x4 and z8 slot connectors actually come open-ended to accept longer card edge connectors.

Not had cause to do it myself but I've seen some of the guys here hack down older / less powerful cards from a 16X to an 8X due to a lack of slots if they just want another couple of outputs without the need for performance. Your right having a pop at the slot probably makes more sense, but I suspect the card was otherwise uneeded and out of warranty whilst the board board was new and still had a few years on it so they'd rather hack up a £20 gfx card than a £150 motherboard!
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