What about the A64 chips prevents use in multiprocessor?

[JHutch]

I've been digging around here and there trying to find some information on why the Athlon64 cannot be used in a dual processor motherboard. I know the Opteron is "designed" for it, but I was wondering if there was a technical reason why it just isn't possible.

JHutch

 

[Eagle17]

well unless you get an fx you will have a hard time fitting the 754pin into the 940pin socket.

as far as designed for, I am by no way an expert however I remember reading something about a processor ID register that needs to be different in order to have multiples. this was back when the first athlon MPs came out and again if memory serves me you could just close a bridge to get a regular athlon to work in mp motherboards.

of course the fx processors are near the same price as the opterons also.

 

[JHutch]

Ok, yes, the pin issue would make a physical connection a little ... hard to manage.

I was thinking more of a technical issue of why it would work on a deeper level. For instance, is the HyperTransport (which I believe is implemented differently between the two) the holding factor?

Basically, if a motherboard maker *wanted* to make a dual A64 motherboard (think back to the old BP6 dual celeron motherboard).... would it be possible? If not, what would be holding them back?

JHutch

 

[Ulukai]

The hypertransport on A64 and opteron are implemented the same way, it's just that the A64 only has one HT link which is used to connect the CPU to the north bridge of the motherboard chipset. The opteron has 3 HT links IIRC, one of which is used to connect to the north bridge and the other two are used to connect to two other opterons.

Edit: Of course, that's only the reason why you can't use A64s in a multi-processor system, I don't know exactly what keeps a 1xx series opteron from working in a 2-way system and so on, if at all.

 

[DivideBYZero]

Found this on ExtremeTech:

Q]Also the Athlon 64 FX includes only a single, active non-coherent HyperTransport link, versus three HT links in Opteron chips (though Opteron 100 series chips have no coherent HT links either, and we suspect the Athlon 64 FX still has all three links in its silicon, with two disabled).[/quote]

Sounds like the answer. HT links turned off in FX. Non-existant in A64.

 

[Jeff7181]

I thought I read somewhere that you can use an Opteron 248 in an 8 way setup, but it's not tested and guaranteed to operate in anything more than a 2 way setup.

 

[DivideBYZero]

Originally posted by: Jeff7181
I thought I read somewhere that you can use an Opteron 248 in an 8 way setup, but it's not tested and guaranteed to operate in anything more than a 2 way setup.

Interesting...

Makes sense, as there would not physically be any more HT links that with 2 way...