[lug] PCI-X question

Gary Hodges Gary.Hodges at noaa.gov
Mon Jul 31 14:52:54 MDT 2006

Zan Lynx wrote:
> On Mon, 2006-07-31 at 10:59 -0600, Gary Hodges wrote:
>>In the next couple/three months I'm planning on buying a new work 
>>computer.  I had all the components pretty much figured out until 
>>yesterday when I realized the SCSI controller I was getting is PCI-X and 
>>the MBs I am looking at don't have that slot.  As an aside, PCI-X slots 
>>seem to be extremely rare in single CPU MBs, and none exist for AMD AM2 
>>MBs best I can tell.  How much of a performance hit will I take running 
>>the card in a regular PCI slot?  I'm wondering if I should just go with 
>>SATA drives since I can't make full use of the card's speed.
> I don't believe every PCI-X card can run in an ordinary PCI slot.  You'd
> want to double check that.
> The performance loss should not be *too* bad.  The speed limit of an
> ordinary PCI bus is 133 MB/s.  After overhead, about 95, I find.
> If you're also running Gigabit Ethernet off the same bus, then things
> will get bad.  PCI video cards would cause the same problem.
> But if it's mostly all alone on the bus, I'd be happy enough with a 95
> MB/s disk speed limit.

Thanks for your comments.  I did double check that the card is backward 
compatible and it is.  The PCI slots are v2.2 so run at 66 MHz.  Does 
that put limit at ~260 MB/s?  The video card will be in a PCI Express 
slot and the NIC (Gigabit) is on-board.  There won't be any other cards.


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