[LUNI] PCI slots 64bit 32bit compatibility

[Ed Jamison]

For an illustration, this card:
http://www.motherboardexpress.com/specs/spec_adv.cfm?ProductID=11323
is 64 bit compatible.  You'll have to look at the image gallery to see 
what the card looks like, but this IS 64 bit compatible.
This cardL
http://www.motherboardexpress.com/specs/spec_adv.cfm?ProductID=4965
on the other hand, is not 64 bit compatible.  This is an easy way to 
tell whether something is compatible or not...

Ed

Don Holmgren wrote:

>On Thu, 1 Aug 2002, Rick Sullivan wrote:
>
>  
>
>>Jay wrote:
>>
>>    
>>
>>>Can I put a 32bit card in a 64bit slot?
>>>      
>>>
>>NO
>>
>>    
>>
>>> I have to guess I can (physically) but will it work? 
>>>      
>>>
>>NO - PCI connector keying prevents this
>>
>>    
>>
>>>That is are 64bit slots backward compatible with 32bit cards?
>>>      
>>>
>>NO
>>
>>
>>
>>But you can plug some 64 bit cards into 32-bit slots. Adaptec 29160 
>>would be an example.
>>    
>>
>
>
>I'm not sure this is correct.  PCI slots and cards have keying for 3.3V
>and 5V compatibility.  It's not possible (physically, because of keying)
>to plug a 5V 32-bit card into a 66MHz 64-bit slot, since that slot
>requires 3.3V cards.  However, 3.3V 32-bit cards should work fine.
>
>Here's a FAQ entry from Compaq on this issue:
>
>   Compaq FAQ: Can I plug my 32-bit PCI cards into the 64-bit PCI slots?
>   (FAQ5379)
>
>   Yes, the 64-bit PCI slots are backward compatible with 32-bit PCI
>cards. A 32-bit PCI device may be plugged into a 64-bit slot and will
>operate as a 32-bit card but will not get any performance benefit from
>being in a 64-bit slot. A 64-bit PCI device may be plugged into a 32-bit
>slot but will have reduced performance as it will operate as a 32-bit
>device instead of a 64-bit one. The 66MHz slots only accept 3.3V PCI
>devices and are not universal like the other PCI slots which will accept
>either 3.3V or 5V devices. These two 66MHz slots are keyed such that a
>device that is not 3.3V cannot be inserted into the slot, so there is no
>danger of damaging devices. Any 66MHz device can be plugged into the
>other universal slots. However, only 33MHz devices that operate using
>3.3V can be inserted into the 66MHz slots.
>
>Don Holmgren
>Fermilab
>
>
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>  
>