Socket 940 is a 940-pin socket for 64-bit AMD server processors. The socket is almost entirely covered with leads with no hole in the middle. There are four spots on the socket which do not have leads, and are used to align the processor correctly. AMD Opterons and the older AMD Athlon 64 FX (FX-51) uses Socket 940. Being an intended server platform, processors using this socket only accept registered, ECC memory, because with servers and workstations, memory errors are less acceptable and cause more damage. Dual Socket 940 boards also exist, allowing the use of multiple 200-series Opterons, and even four or eight-socketed boards are in existence. The Socket 940 platform is designed for professional accuracy, not speed or bleeding-edge gaming performance.

There is a new 940-pin socket called AM2. Though the current Socket 940 and the M2 both share the same number of pins, they are not pin-compatible. That is, a Socket 940 processor will not fit in a AM2 socket. The same is true in reverse; a Socket AM2 processor will not fit in Socket 940. The reason for this is due to the fact that all 64-bit AMD processors, unlike all current Intel processors, include the memory management functionality not as a discrete chip on the motherboard, but rather on the CPU die itself. That means that, if someone wishes to utilize a newer type of memory (e. g. DDR2 vs. DDR), then AMD would need to manufacture an entirely new microprocessor with entirely new memory management electronics built into the chip in order for that newer memory to be useable. This is exactly the situation here; Socket AM2 is designed for DDR2 memory, whereas Socket 940 is designed for DDR (occasionally called "DDR1") memory. This issue highlights one of the disadvantages of including the memory management functions on the CPU die itself. However, performance benchmarks suggest a significant performance increase by doing so, hence AMD's decision to take this design route.

For somewhat related reasons, Socket 939 processors cannot be used in Socket 940 motherboards, even though both Socket 939 and Socket 940 CPUs support the same DDR (aka "DDR1") memory. The distinction here is that Socket 940 requires more expensive registered memory, whereas Socket 939 uses less expensive unregistered memory. There are also issues of electrical capacitance which lead to four-layer vs. six-layer motherboards (the latter are slightly more expensive to manufacture), which was the reason for the genesis of Socket 939; Socket 940 requires six-layer motherboards. This pin-incompatibility was known to cause some frustration when AMD moved the Athlon 64 FX processor, their premier gaming platform, from a Socket 940 (Opteron 1xx) basis to Socket 939; users who wanted more speed needed to purchase and install an entirely new motherboard. AMD's motivation for Socket 939 was entirely driven by perceived total system cost. However, even after this socket change, the Athlon 64 FX series remained a relatively high cost option, even at times slightly higher than a comparable Socket 940 Opteron. Given the Opteron's excellent performance, it was not unheard of for Socket 940 Opteron 1xx sales to actually cannibalize Athlon 64 FX sales, even at times among the FX's target market, gamers.

Given AMD's recent proliferation of CPU socket platforms, questions about Socket 940's longevity abound on the Internet. Socket 940 was, from the start, primarily geared toward server and higher-end workstation markets, where purchasing decisions are traditionally conservative and customers are known to depreciate (and thus use) their existing gear over at least a five-year cycle. Thus, AMD's plans for Socket 940 stretch out several years into the future, and longevity for this platform is expected to be relatively long. As an example, Socket 5, made famous by the Intel Pentium processor, was in active manufacture, in various backwards-compatible forms including Super Socket 7, for over five years. Socket 370, championed by Intel's Pentium III and Celeron lines, lasted for a similar time frame.

Note that, regardless of the socket form factor, all 64-bit AMD processors will run all of the same software; they are all fully binary-compatible.

Socket 940 motherboards are currently available with the following chipsets:

• AMD's own 8000-series
• VIA K8T890
• nVidia nForce3 Ultra
• nVidia nForce4

Socket 940 motherboards are currently available from many manufacturers, including:

• ASUSTek International
• Micro-Star International
• Gigabyte Taiwan
• Tyan Computer Corporation

Additional information

• AMD Product Information
• AMD Technical Details for Athlon64 and Athlon FX
• Introduction to DDR RAM

CPU sockets

Sockel 940 | Socket 940 | Socket 940