PCI slots
 

Hi just a quick (possibly dumb) question:

My linux router box's motherboard has 4 PCI slots. I have 2 RealTek 8139 based network cards.

Is there any preference as to which PCI slots I should use for the cards? Ie, slots 1 and 3, slots 1 and 2, or whatever? Is it best to keep the cards in adjacent slots, or separate them?

Cheers

Duncan

Nope. However, putting cards in every other slot helps in stablity problems.

really now .. is this because of the IRQs that the slots use?

I know certain slots share IRQs.... However, irrespective of what slots i put my PCI cards in, they always have the same IRQs! (10 and 11)

Duncan

To be honest, the only time I've ever noticed any problems with putting things next to eachother is when a) you put a GFX and SFX card next to eachother (physical interference problem) or b) when you put two GFX cards next to each other (sharing IRQ problems).

Other than these, I've never run into problem with other types of cards being put next to eacher - indeed, I've had 2 NICs next to eachother on a number of occasions.

Spacing the cards makes the system more reliable. This is because of data and electrical lines. Sometimes there is peaks and dips when data is tranmitted and recieve instead of being constant data flow. The space softens the dips and peaks. IRQs doesn't have anything to do with it. If the expansion card can handle shared IRQs, then you won't have any problems. Software that controls the device will use the IO address instead of IRQs. Sometimes the BIOS assign an (one) IRQ to two or more devices. You can change that by manualing assigning the IRQs. LINUX will still work if two or more devices are using the same IRQ.

Usually PCI 1 is for MPEG cards, but today's graphic cards takes up that slot from the huge heatsink and fan. Though computers are now fast enough to do MPEG at high resolutions in real time.

Not sure I really under stand your reasoning.

Radio frequency interference (RFI) which the farther the cards are apart the less likely they will be affected by each other.

However, the noise that is present on the power and data lines would be present on all PCI cards since these lines are common to all. So data going to PCI slot 4 is going to be seen by slot 1.

A poorly designed video card might be a problem but most other I/O cards shouldn't be.

However, spreading the cards might provide better airflow which will keep the PC cooler and therefore be more stable.