PCI 64-bit 66MHz (3.3-volt) vs. 32-bit 33MHz (5-volt)

[hausdave]

I understand that 64 bit pci cards cannot go into 32 bit slots but what about the other way around? Can someone give me a quick lesson on this subject?

 

[AndyHui]

They won't go in the other way around because of the orientation notch.

If you have a look at 64-bit 66MHz slots, (and ignore the length), they are backwards compared to the standard 32-bit 33MHz PCI slots.

 

[hausdave]

Thank you very much Andy. I appreciate it. I have only ever installed one 64 bit PCI card and it was almost two years ago.

 

[SCSIRAID]

64 bit PCI cards CAN go into 32 bit slots as long as the 64 bit card is keyed for 5V or universal operation. I have a 64 bit Adaptec 160 card running in a 32 bit slot right now.

Cards can be keyed (by the slots or notches in the connector) to work in 5V slots, 3.3V slots or both (universal). 66Mhz is by default 3.3V. 33Mhz can be either but is usually 5V. Slots on the other hand are keyed as either 5V or 3.3V but NOT both. If the card doesnt have a cut in the connector where the slot has a key blocking that area then the card wont fit. For example if you have a 32 or 64 bit card that requires a 5V bus... It wont plug into a 64 bit connector keyed as a 3.3 V interface. A universal card has 'cuts' or "notches" in both the 3.3 and 5 volt positions.

Andy - The connector is not backwards... the key is just in a different position (indicating 3.3V instead of 5). There is a 5V 64 bit slot that looks just like the 32 except its longer.

 

[AndyHui]

Yes, I know the slot is not actually backwards....I couldn't come up with a better description on the spot for a moment though. Thanks.....it's been a long day for me.