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May 25, 2006
AMD releases socket AM2
AMD released the new AM2 socket to the public on May 23rd. Motherboards and processors using the new socket are now available to the public. This new socket has 940 pins, but is different from socket 940 and chips are not interchangeable between the two socket types. Most processor models that were available for socket 939 are now available for AM2. The primary reason for the new socket is so that AMD chips can now support DDR2 memory as Intel chips have for some time now. Using DDR2 theoretically improves the speed of memory access as well as memory bandwidth. But, in practice, is this really a step up? The short answer is that, if you're getting a low end or mid-range system, you'll probably do better sticking with socket 939 for the time being. For the high range, however, there are significant improvements in performance with the new socket.
The first reason for this inconsistency in performance increase applies to both AMD and Intel and has to do with the current state of DDR2 memory itself. Despite its higher clock speeds than plain DDR, DDR2 has been suffering from higher CAS latency than DDR memory since its inception. CAS latency is basically overhead that has to be done every time memory is accessed. It makes a big difference for lots of small accesses to memory and a smaller difference when dealing
with large blocks of memory. In some cases, this can largely negate the higher clock rate. Newer DDR2 ram is coming out with lower CAS latencies, but you can expect to pay a premium for such parts.
The second reason is due to a difference in where AMD and Intel put their memory controllers. For Intel, it's off the chip, but AMD uses an on-chip controller. There are advantages to using an on chip controller, but with DDR2 memory, AMD has run into a limitation of their approach. Access to the memory is now being limited by the clock speed of the processor. There is a threshold point at around 2.6 GHz where the real potential of the DDR2 memory is opened up. Currently, only two of the AM2 processors, the Athlon 64 X2
5000+ at 2.6 GHz. and the Athlon 64 FX-62 at 2.8 GHz reach the neccessary speeds. For the chips lower than that, performance is pretty close to the socket 939 version of the same chip with DDR memory. For some of the lower end models, the AM2 version with DDR2 may actually have worse performance.
This is to be expected with a newer technology. Intel ran into similar problems with the switch to DDR2 and now AMD has its turn. Very soon, AMD will be switching from its current 90 nanometer manufacturing process to a 65 nanometer manufacturing process. At that point, processor clock rates should be able to go even higher, and new processors using the AM2 socket should be the clear winners across the board over socket 939.
For the time being, if you're willing to pay top dollar, the AM2 version of the Athlon 64 FX-62 appears to be the most powerful processor you can buy. If you're not looking for a mega powerful PC, however, it's probably best not to be an early adopter of the AM2 socket. You'll get just as much computer, and more value for your money, with socket 939.
For a review of socket AM2, take a look at http://www.tomshardware.com/2006/05/23/amd_reinvents_itself/.
Posted by Kieran at May 25, 2006 12:08 PM