PCI in PCI-X

[Logistics]

I'm not well educated on the nuances of utilizing PCI-X slots. Does the entire length of the slot run at 133MHz if it's a 133MHz PCI-X slot or does only the added, back portion run at that speed.

I'm wondering if there are PCI cards, specifically video cards, which will utilize the front half of a PCI-X slot, but still run at the full speed of the PCI-X slot.

The best thing that seems to remain in the PCI world is the Geforce 8400GS, which claims to miraculously be able to play full HD video. (I only question this because I thought more bandwidth would be required to do this.) Do you suppose manufacturers of this card have designed it to be able to run at the 133MHz of a PCI-X slot?

Any info would be appreciated as this is an area I am foggy on.

-Logistics

[brethin]

Re: PCI in PCI-X

There are many different speeds of PCI-X slots ranging from 33MHz to 266MHz depending on the board its on. Never asume because its PCI-X its 133MHz. Unlike say PCI which is 33MHz or AGP which is 66MHz PCI-X uses many different speeds depending on the board they are on. ANY PCI-X card placed in a PCI slot (and yes there are many) will run at the PCI rate. So sticking a PCI-X 266MHz card in a standard PCI slot will drop it to 33MHz if the card supports running in a half slot (or PCI vs PCI-X slot).

[mariushm]

Re: PCI in PCI-X

No, the card runs at 33 Mhz PCI 32 bit. The 133 MB/s shared between all pci slots is plenty for a video card.

The way the card can decode HD video is through a hardware decoding chip on it. The driver sends the compressed frames to the chip, chip decodes them and puts the output in the video card memory and the driver can then overlay that frame over the screen image. The image doesn't have to be sent back to the computer so there's no heavy transfers across the pci.

You can put pci cards into pci-x slots but the majority of the cards will support only the 32bits side. Some video chipsets may auto detect the pci-x and run on 64 bit bus... thinking of workstation aimed video chips.

[ratdude747]

Re: PCI in PCI-X

The main difference between the two for your purposes is the voltage. Regular PCI is normally 5V, while PCI-X is normally 3.3V. As a result, the key in the slot is in a different position for each.

Few PCI cards are 3.3V only. However, many have two keys cut in them and are thus dual voltage (3.3V and 5V).

If it fits in the slot (correct voltage key), then it should. (I did it to my main rig with a 1394 card).

If not, then it obviously will not work.

Beware of cards that hare "double keyed" but are not actually dual voltage. I have an old higher-end diamond sound card that is like that. It's stupid but for whatever reason once in awhile you come across a dumb design like that.

The way you tell is to try the card in the slot. If it POSTs and the card shows up in the OS, you're good. If not, then it's not really dual voltage and not usable in a standard PCI-X slot. Don't worry, getting the wrong voltage in a PCI-X won't kill anything since at worst you are putting a 5v card in a 3.3V slot.

Data wise, PCI-X was meant to be backwards compatible from day 1. This also works for PCI-X cards that are dual keyed; they will usually work in a regular PCI slot running as a regular PCI card, provided that the particular shot has no components nearby that get in the way of the extra unused connector.

Hope this helps. If not, I have some spare/Junk parts that I can use to make some tutorial pictures.

[brethin]

Re: PCI in PCI-X

NO PCI card will ever run at anything other than 33MHz (unless overclocking the PCI buss) no matter what slot you put it in (and no sticking a PCI 33Mhz card in a PCI slot on a 266MHz PCI-X buss will just make that buss run at 33MHz). If you put a PCI card in a system with a PCI-X buss running at 266MHz it will slow down and make the buss run at 33MHz. This is why many server boards had multiple PCI-X busses so you could group the cards in the slots per buss based on the cards speeds and not cripple all the slots because of 1 slow card.

[ratdude747]

Re: PCI in PCI-X

NO PCI card will ever run at anything other than 33MHz (unless overclocking the PCI buss) no matter what slot you put it in (and no sticking a PCI 33Mhz card in a PCI slot on a 266MHz PCI-X buss will just make that buss run at 33MHz). If you put a PCI card in a system with a PCI-X buss running at 266MHz it will slow down and make the buss run at 33MHz. This is why many server boards had multiple PCI-X busses so you could group the cards in the slots per buss based on the cards speeds and not cripple all the slots because of 1 slow card.

True... That may explain some oddities regarding my personal setup although removing the pci card int he PCI-X slot made no difference.\

That said, if the OP isn't using any PCI-X cards, who gives a darn if his PCI-X bus speed slows down?
.

[Logistics]

Re: PCI in PCI-X

True. My board has a single 133MHz PCI-X slot, two 100MHz and a single PCI slot. I'm not worried about slowing the bus down, I just thought I would need to make an attempt at more bandwidth so the system could genuinely put out real HD video. However, I believe my TV is only a 720p rig so I don't need HD in 1080. Now, I just need to find said card in low-profile so I can stick it in the rack server I just bought.

[homerging]

Re: PCI in PCI-X

Beware of cards that hare "double keyed" but are not actually dual voltage. I have an old higher-end diamond sound card that is like that. It's stupid but for whatever reason once in awhile you come across a dumb design like that.

I can remember much the same problem affecting some early AGP cards. Put them in the wrong motherboard and things would go very badly.

[japlytic]

Re: PCI in PCI-X

As far as I know, PCI-X (not Express) slots have only been used in workstations and servers.

[ratdude747]

Re: PCI in PCI-X

As far as I know, PCI-X (not Express) slots have only been used in workstations and servers.

Powermacs used them. I also know of desktop boards that used them (the Supermicro PDSGE in my dad's rig has 2).