What determines if a CPU supports a multi-CPU motherboard?

I'm curious if the extreme platform ever supported a multi-CPU setup. I'm assuming there is something on the CPU itself that determines whether or not that is possible.

I understand that most Xeons support a multi-CPU configuration, but has that ever been possible with the Extreme platform (for instance, the Haswell-E that was just released).

I'm guessing that Intel only reserves that for the business class of CPUs, but it would be nice to have that capability with something like the Haswell-E.

Another question:

Will the Haswell-E X99 support 128 gigabytes of RAM once 16 GB DDR4 Simms are released to the market? Or does that top out at 64 gigs?

Will the Haswell-E X99 support 128 gigabytes of RAM once 16 GB DDR4 Simms are released to the market?

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I say yes.

I'm guessing that Intel only reserves that for the business class of CPUs

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Intel reserves this for the xeon chips (e5 -2xxx or e5-4xxx or e7) and it does so by disabling that functionality in the enthusiast chips since both are made from the same silicon as the e5 chips. The xeon E5-1XXX chips also are single socket.

Imtel disables the QPI links necessary for dual CPU operation on i7 and E5-1600 SKUs, which disables dual CPU functionality. Also, IIRC, a dual CPU motherboard BIOS will most often not contain the microcode of processors that are intended to run only in single CPU operation (although there have been some exceptions).

Yes, very very few desktop cpu allowed muti-cpu usage, there has been exceptions, but suffice to say it is very much an exception for desktop grade chips, not to mention the massive cost of using dual cpu. Not that long ago somewhere on the forums someone was asking a similar question, overall is simply not worth it mainly due to scaling. Most stuff the average user does simply does not scale to single cpu lots of cores let alone trying to feed 2 cpu with double that amount.

Last one that could do this was one in the i7 900 series or some such thing like that if I recall (has to have dual QPI links for send and receive) though there are of course lower cost xeon (such as 5500-5600 and the EVGA SR2 board) few motherboards that were made are dual socket A and B massive as well. SR2 could run single cpu or double buddy of mine ran single 980 on his but seems kinda pointless to do so xd.

8 dimm 16gb stick max of 128gb apparently on X99.