While I was reading the Dutch hardware site I came accros this interesting article:
http://blogs.mercurynews.com/aei/2006/06/amd_puts_pressu.html#more

AMD Is gonna build a socket for 2 Athlon64 X2 CPU's but should I see that as one entire socket for 2 Dual Core prox or 2 sepperate sockets for each one dual core CPU?

Anyways I don't see the point in this since QuadCore will be arriving soon and I dunno if it's better to have 2 sepperate Dual Core procs or just one Quad Core Proc qua Economics?

If you want such a PC you have to buy a special mainboard with two Socket 939.

Until now every Socket 939-CPU had only one non-coherent Hypertransport-channel so they couldn't be connected together without special hardware. In Opteron 2xx- and 8xx-series you have three Hypertransport-channels which are partially coherent (Opteron 2xx: one coheren HT-channel, Opteron 8xx: all three channels are coherent).
Since the cores of the Athlon 64 and the Opteron are basically almost the same but partially deactivated (HT-channels for instance) at the Athlon 64, AMD can activate a coherent HT-channel at the Athlon 64, too.

Basically it's the technology of the Opteron which enters "normal" desktop-PCs.

Here is a german newsticker which has a drawing of the principle of the 4x4-socket.
In the [Update:]-section is written that - different from earlier speculations - the 4x4-technology is able to split the controlling of the memory to both CPUs so the CPUs don't have to share memory like all Intel-CPUs.

wauw that's brilliant :) can't wait to see Athlon64 X4 cpu's then hay ;D hehe

If anyone has an Airbus full of cash, please deliver to my address so I can buy one of these mainboards! ::)

LOL! ;D

hahaha the A380 , hmm why not an Antonov AN225 of Gold wiieeee ;D hahaha

anyways yeah Quad CPU is possible on the Tyan Tiger K8W :)  2x dual core Opteron then Quad Core is worth do'n okay there are real 4 way board but to beable to obtain one of those may not be the problem it's the CPU's needed the Opteron 8.xx series arrgghh :-X by buy'n 4 of those then the fun dissapears rapidly.