PCI in a PCI Express x16 slot?

Dralnu · Veteran Joined: 24 May 2006 Posts: 1919

Are PCI slots backwards compatable, or not?
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d2_racing · Posted: Fri Jun 22, 2007 2:48 am Post subject:

If I trust my instinct...no

SiberianSniper · Posted: Fri Jun 22, 2007 2:59 am Post subject:

no, they're not, but there are adaptors, for example http://www.magma.com/

Dralnu · Veteran Joined: 24 May 2006 Posts: 1919

I didn't think they would. Issue with too much power or what?
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The day Microsoft makes a product that doesn't suck, is the day they make a vacuum cleaner.

crazycat · Posted: Fri Jun 22, 2007 4:09 am Post subject:

pci is parallel, wile express has serial architecture. PCI-express also needs less wires. They are only software compatible.

Dralnu · Veteran Joined: 24 May 2006 Posts: 1919

d2_racing · Posted: Fri Jun 22, 2007 11:25 am Post subject:

When the data is send :

serial output : 11101010101010101010101010

parallel output :

1
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0

So you send data from multiple chanel instead of one.

crazycat · Posted: Fri Jun 22, 2007 5:02 pm Post subject:

Parallel(PCI) is actually better because it sends more at once, BUT it's speed is limited since you have to send and syncronise accross a lot of wires, since the length of wires is sometimes different. With serial, you just have a pair of wires, but since you don't have to syncronise it you can just send it at a very high frequency. Anyway, with pci express you theoretically have less complexity/wires so it should be cheaper to build mainboards with it. Also the whole pci bus sits on the same "lane", like 2 ide drives on master/slave. So the data which is send to one device is send to all of them, so with each new PCI device you have less brandwith. With pci-express, it has 16 or 20 or even more "lanes" each of which is a dedicated data link and most gpu's can use up to 16 of such lanes at once. I dont remember it exactly, but i think each lane is 2times as fast as pci(32bit/33mhz) bus, which ,if i remember it correctly, has only 66mb/sek max brandwidth.

Dralnu · Veteran Joined: 24 May 2006 Posts: 1919

So the x16 is how many serial lines it has running then? Kinda like parrallel, but using serial connections?
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The day Microsoft makes a product that doesn't suck, is the day they make a vacuum cleaner.

think4urs11 · Posted: Fri Jun 22, 2007 11:38 pm Post subject:

John R. Graham · Posted: Fri Jun 22, 2007 11:47 pm Post subject:

PCI Express is scalable serial. Each serial channel (called a lane in PCIe patois) is 2.5Gbits/sec. The x16 means that 16, 2.5Gbits/sec lanes can be engaged in that slot for an aggregate throughput of 40Gbits/sec (5Gbytes/sec) theoretical bandwidth (overhead limits it to about 4Gbytes/sec). There are also 32 lane slots for up to 8Gbytes/sec actual throughput.

This is far faster than conventional parallel PCI (32 bits wide, 33 million transfers/sec: 0.13Gbytes/sec.

Simple peripherals (parallel port, ethernet card) can use a single lane and benefit from the cost reduction of smaller connectors. But, PCIe is why you don't see AGP connectors on new motherboards: it's so fast that you don't need AGP.

- John

Dralnu · Veteran Joined: 24 May 2006 Posts: 1919

Eh, some mobos DO still have AGP.

Thanks for all the info. I think I may look up AGP myself this time. Maybe this should be renamed and thrown somewhere for future refrence for others? (Maybe Docs?)
_________________
The day Microsoft makes a product that doesn't suck, is the day they make a vacuum cleaner.

John R. Graham · Posted: Sat Jun 23, 2007 12:50 am Post subject: