Verdict: DDR2 does nothing for the athlon 64
While Intel is guilty of changing its CPU packaging and chipsets with almost every new CPU launch, AMD has been more conservative. For example, it introduced dual-core CPUs on the existing Socket 939 packaging, which meant that people didn't need to upgrade their motherboards. However, despite the success of Socket 939, AMD has finally decided to ditch it in favour of a new socket, Socket AM2, for its new range of Athlon 64 CPUs that support DDR2.
Physically, Socket AM2 has one pin more than Socket 939, making 940 pins in total. But hang on a minute, didn't the original Athlon 64 FX-51 launch on Socket 940? Yes it did, but confusingly, Socket 940 and Socket AM2 aren't compatible with each other. The reason for this is that Socket AM2 is designed for AMD's new Athlon 64s, which have a DDR2 memory controller, while Socket 940 chips required registered DDR, and Socket 754 and Socket 939 CPUs had single- and dual-channel DDR controllers respectively.
AMD hasn't stated why it decided to switch from DDR to DDR2, although high-end DDR2 memory does provide higher bandwidth than DDR. For example, Socket AM2 supports up to PC2-6400 (800MHz) DDR2. DDR2 also runs at a lower voltage than DDR, so it consumes less power. However, most DDR2 DIMMs have much higher latency timings than DDR modules, which can negate any advantage gained from higher bandwidth. In all other regards, Socket AM2 chips are the same as Socket 939 chips, as they're made on a 90nm process, run at the same FSB speed, and have the same amount of cache and features.
Although AMD plans to produce all future Athlon 64s using the Socket AM2 format, the first chip off the production line was the flagship Athlon 64 FX-62. The FX-62 is clocked at 2.8GHz, 200MHz faster than the Socket 939 FX-60. This latest FX directly replaces the previous model, so it should sell for the same price - a wallet-mashing £705. As with all Athlon 64 FX chips, the FX-62 has an unlocked CPU multiplier.
To see what effect DDR2 memory has on performance, we tested the FX-62 in the MSI K9N SLI Platinum against an FX-60, multiplier-overclocked to 2.8GHz, in a DFI Lanparty UT NF4 SLI-DR Expert board. The FX-62 system was equipped with 1GB of Corsair XMS2-5400UL RAM with 4 - 4 - 4 - 15 timings, and the overclocked FX-60 with 1GB of Corsair XMS4400C25 with 2.5 - 4 - 4 - 8 timings. All of the other components in the two test systems were identical.
Socket 939 Athlon 64s benefit more from lower-latency RAM than from greater bandwidth, so it came as no surprise that, at the same frequency, the FX-62 system was marginally slower than the FX-60 system. For example, in the memory- and disk-intensive Paint Shop Pro and multitasking tests, the FX-62 was around 2 per cent slower than the FX-60. This isn't a massive difference but, given that the FX-62 is supposedly more advanced, it's disappointing. In the CPU-intensive TMPGEnc DVD encoding benchmark, both systems performed identically, which is predictable, given that this test doesn't rely on memory performance.
Unfortunately, the only Socket AM2 motherboard available to us was the MSI K9N SLI Platinum, which is a poor overclocker. Thus, we were only able to overclock the FX-62 to 3GHz, which was achieved by raising the clock multiplier from 14x to 15x. At 3GHz, the FX-62 pulled ahead of the overclocked 2.8GHz FX-60 system, but the difference is hardly earth-shattering.
CONCLUSION
Our benchmarks suggest that high-latency DDR2 memory has an impact on the performance of the AMD64 architecture, which means that the FX-62 is slower than an equivalent-speed Socket 939 CPU with DDR. However, the difference is slight, and less than many pundits predicted. But there's no escaping the fact that, clock for clock, a Socket AM2 system will be slower than a Socket 939 system, so there's no incentive to upgrade.
In concert with the disappointing debut of the nForce 570 chipset, things aren't looking good for AMD. Considering that an upgrade from Socket 939 to Socket AM2 would require a new motherboard, CPU and RAM, you'd be mad to buy the FX-62 now, especially as Intel's new Core2 Duo CPU is only a few months away.
