Socket 940 is only used by the Athlon 64 FX and Opteron-line, Socket 754 is for the plain Athlon 64.
Socket 940 processors have a 128-bit 'dual-channel' memory controller, whereas Socket 754 processors only have a 64-bit single-channel memory controller.
However, Socket 940 motherboards require registered memory which is a bit slower and more expensive than normal unbuffered(non-registered) memory.
The Athlon 64 FX is targeted at enthusiasts - it offers superior performance and easy overclockability(fully unlocked multipliers), but costs significantly more than a plain Athlon 64.
For most users, the 'normal' Athlon 64 offers more than enough performance...it also supports Cool 'n' Quiet
' ">http://www.amd.com/us-en/asset...nstallation_Guide3.pdf, a power-saving feature which helps to reduce both noise and power-consumption
Eventually, both the Athlon 64 and Athlon 64 FX will be moved to the upcoming Socket 939 while the Opteron will remain on Socket 940.
ALL Socket 939 processors will have a dual-channel memory controller and can use unbuffered memory.
The opinions expressed above do not represent those of Advanced Micro Devices or any of their affiliates.
AMD Athlon 64 X2 6000+ 89W :: Asus M2N32SLI Deluxe :: 2x1024MB Muskin XP2-6400 DDR2-800 :: BeQuiet! Darkpower Pro 530W :: 2x WD Raptor 74GB/10k rpm, RAID 0 :: ATI Radeon X1950XTX