Socket 940

Socket 940 is a 940-pin socket for 64-bit AMD server processors. The socket is entirely covered with leads, except for four key pins used to align the processor. AMD Opterons and the older AMD Athlon 64 FX (FX-51) use Socket 940. Being an intended server platform, processors using this socket only accept registered memory, because, in servers, memory errors are less acceptable and cause more damage. [cite web|url=http://www.short-media.com/articles/socket_940_vs_939|last=Kronlund|first=Doug|date=2004-06-27|publisher=Short-Media|title=Socket 940 vs. 939|accessdate=2007-01-28]

The more common use of Socket 940 is in the Server market.Dual Socket 940 boards use the 200-series Opterons.Four-socket (common) or eight-socket (rare) boards use the 800-series Opterons.The Socket 940 platform is designed for raw power and professional accuracy, not bleeding-edge gaming performance.

There is a new 940-pin socket called AM2. Despite having the same number of pins, Socket 940 and AM2 are not pin-compatible. This means a Socket 940 processor will not fit in an AM2 socket and vice versa. The reason for this is because 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. [cite web |url=http://www.tomshardware.com/2006/05/23/amd_reinvents_itself/page2.html |title=AM2: AMD Reinvents Itself |accessdate=2007-01-28 |author=Bert Töpelt |coauthors= Daniel Schuhmann, Frank Völkel |date=2006-05-23 |publisher= Tom's Hardware Guide] 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 usable. 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 "unbuffered" 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.Fact|date=August 2007 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.Fact|date=August 2007

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.

Chipsets

Socket 940 motherboards are currently available with the following chipsets:
*AMD's own 8000-series
* [http://www.via.com.tw/en/products/chipsets/k8-series/k8t890/ VIA K8T890]
* [http://www.nvidia.com/page/nf3.html nVidia nForce3 Pro]
* [http://www.nvidia.com/page/nforce_pro.html nVidia nForce4 Professional]

Socket 940 motherboards are currently available from many manufacturers, including:
* [http://www.asus.com/ ASUSTek International]
* [http://www.msi.com.tw/ Micro-Star International]
* [http://www.gigabyte.com.tw/ Gigabyte Taiwan]
* [http://www.tyan.com/ Tyan Computer Corporation]

References

External links

* [http://www.amd.com/us-en/Processors/ProductInformation/ AMD Product Information]
* [http://www.amd.com/us-en/Processors/TechnicalResources/0,,30_182_739_7203,00.html AMD Technical Details for Athlon64 and Athlon FX]
* [http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/25766.pdf AMD Socket 940 Design Specification]