[lug] PCI-X question

D. Stimits stimits at comcast.net
Tue Aug 1 22:58:08 MDT 2006


>>> 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.
>> The real question is, do your video, NIC, and PCI slots share the 
>> same data path to the CPU?  More at:
>> http://www.samag.com/documents/s=9408/sam0411b/0411b.htm
> Thanks Dave.  I just read the article.  The writer convinced me that 
> Opteron systems implemented correctly are good.  The AM2 seems to be 
> an update of the 939 CPUs to take advantage of DDR2 memory.  Lots of 
> details and it starts getting confusing to me, but I think I'm 
> somewhat safe in assuming the good things about 939 have been rolled 
> into AM2.
Opterons are extreme good performance :P

The AM2 that is upcoming is almost the same as the socket 939. The real 
difference is in the memory...the AM2 will support faster memory. The 
opteron is probably the only chip out there that will actually be able 
to take advantage of that much bandwidth.

> In reply to D.Stimits.  I only looked at a couple sites (Newegg and 
> mwave), but I only found two single Opteron MBs with PCI-X and neither 
> have PCI Express.  It seems PCI-X and PCI Express are mutually 
> exclusive on single CPU MBs.  I saw a couple ~$500 SMP boards with both.

Yeah, I think you'll find that PCI-X is geared towards "server" boards 
with high end raid or fiber channel, maybe myrinet or some network that 
is beyond gigabit. The PCI-e is geared towards screaming workstations. 
The two are not exclusive of each other, but I think most of the 
motherboard manufacturers decided those who want PCI-e would like a pair 
of SLI slots, and they didn't have room to also add PCI-X without 
cutting something out...and sending the board beyond the price of even 
the high end desktop buyers. PCI-X also tends to be easier to implement 
on 32 bit cpu systems when they use SMP with the interleaved memory 
(you'll notice on those boards with PCI-X they most often tell you that 
memory must be installed in matching pairs).

If it is the cost of the cpus that is the worst part of it, you should 
know that SMP boards (in most cases) work perfectly well with just 1 cpu 
installed. You could buy any dual cpu board and not fill the 2nd cpu slot.

D. Stimits, stimits AT comcast DOT net

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