Lennart Sorensen wrote:
On Sat, Jul 23, 2005 at 12:01:27PM +0200, Michelle Konzack wrote:
I had a MSI K8D Master3 (380 Euro, Two Opteron 240) which drived me
crazy and I have tried to run one of those CPU's on a Singel-Opteron
mainboard from Tyan and it does not work.
Then I have bought two Tyan Dual-Opteron Boards andused it with only
one CPU each, which works very fine.
Then I have tried to run a Opteron 142 on a Dual-CPU-Board and it does
not work.
So you NEED the right CPU to your Mainboard. You can not use a 1xx on
a Mainboard which was made for a 2xx.
I wonder if that is for technical reasons, or just lack of cpu support
in the bioses.
Len Sorensen
The Opteron 1xx series of processors are basically conventional Athlon
64 939-pin processors with an extra pin.
The Opteron 2xx and 8xx series, however, are different--they both have a
different count of what is called "coherent HyperTransport links." These
links are used for transferring SMP protocol type things (cache
coherency checks, cache snooping, etc) between processors. The 2xx
series has one of these links (it can connect to one other processor),
while the 8xx has three. This is the reason why you can't use a 1xx
processor in a 2-CPU system, or a 2xx processor in a 4 or 8-CPU system,
but can use an 8xx processor everywhere (the extra coherent links just
will not be used).
If processors are different speeds I'd imagine there'd be problem with
the cache coherency checking. A processor that is significantly faster
could in theory change the contents of the cache in the mean time the
other processor is receiving information about the first's now defunct
state. SMP has safeguards for this, but AFAIK they rely on the
processors being the same speed. There are probably engineering things
you can do to avoid problems with mismatched speeds, but since very few
people use mismatched processors I don't think this is a manufacturer's
concern.
I'd have to agree with the consensus about dual-core and single-core
mixing--there doesn't appear to be any technical barrier for it not to
work. But I know I don't have the money or need to try it. I'm not sure
how things will behave when the number of processors are not a power of
2, though.
Samat
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