Which motherboard does have different PCI slots on different PCI buses ?

[ZoltPao]

Hi everybody,

I have a high-end ADC card that uses all ressources of the PCI bus when I acquire data. All other cards on the PCI bus are freezed. It is impossible to use this card with a PCI video card, the video card must be plugged in a AGP slot.

I want to use this ADC card on a separate PCI bus than the other PCI cards. Therefore, I am looking for a motherboard that have mutliple PCI buses. I do not even know if such card exist. (The price is not really a problem).

Thanks,

 

[Peter]

You'll have to get yourself a server mainboard whose chipset offers two PCI busses. This is easily recognized by the presence of 66-MHz PCI slots in parallel with 33-MHz slots.

Lower level mainboards use PCI-to-PCI bridging chips to increase on the number of slots - yet these busses are hanging off the one main PCI bus, and a card eating all the bandwidth while transferring to/from main memory will still do so when behind a bridge.

Regards, Peter

 

[ZoltPao]

Thank you very much for your suggestion.

Two subsequent questions:
- Can I plug a 33 MHz PCI card in a 66 MHz PCI slot?
- Any idea of brand / model?

Regards,

 

[Peter]

You can plug a 33 MHz PCI card into a 66 MHz PCI bus, but this will make the entire 66 MHz bus revert back to 33. You can also plug 64-bit PCI cards into 32-bit slots, and vice versa.

As to what brand and model, no idea. Just stay away from Intel 840 chipset.

Regards, Peter

 

[ZoltPao]

Thanks,

it seems that the only other chipset supporting 66 MHz PCI slots
is the ServerWorks chipset. Asus has a mainboard based on it.

Regards,

 

[ZoltPao]

For your information:

There are three different parameters for the PCI cards
- speed: 33 MHz and 66 MHz
- voltage: 5V and 3.3V
- data path width: 32 bit and 64 bits

The 3.3V PCI slot does not use the same slot. It is the 5V slot
rotated of 180°. Therefore you cannot plug a 5V in a 3.3V slot.

A 66 MHz speed requires a 3.3V slot. You cannot plug
a standard PCI card (5V, 33MHz and 32 bits) in a 66 MHz slot.
(This taken from the PCI 2.1 specification p. 222).

So, a 66 MHz bus does not solve my problem because I cannot use
it.

Regards,

 

[ZoltPao]

However, it seems that some board manufacturers made
66MHz and 64 bits PCI slots with 5V. This is the case of Asus
with their mainboard CUR-DLS. (I do not know how thye manage
to do that because it clearly violates the PCI specs).

Regards,

 

[Peter]

On second thought, this does not violate the PCI specification. Assuming that all 5V PCI cards are 33 MHz (a valid assumption given that 66 MHz cards must be 3.3V), you'll never run the bus at 66 MHz with a 5V card present - so you either run the 66 MHz PCI at 3.3V with 66 MHz cards, or you run it 33 MHz with either 5V or 3.3V 33 MHz cards.

Regards, Peter

 

[ZoltPao]

I disagree with your analysis.
You cannot plug a 3.3V card in a 5V slot because the slot is incompatible. This is the case on the Asus mainboard where
you cannot plug a 3.3V card.

Regards,