New Socket AM2 With DDR2

AMD now supports DDR2 memory; almost two years after Intel's switch to DDR2 for its complete range of desktop platforms, AMD is at last following suit. It's high time for the switch, too, because the market is already glutted with DDR2 memory.

AMD's solution has a big downside, however: in contrast to Intel's platform, the memory interface was integrated into the CPU, so there's more to the switch than just a change of chipset. The migration of the memory interface from the chipset Northbridge to the CPU has also produced a few problems:

• The processor core needs changing
• A new socket is required

All of this poses questions about why AMD waited until now to implement DDR2 technology. We see three possible theories:

• DDR2 memory was initially very pricey, which would have made the AMD platform less attractive compared to Intel.
• Memory manufacturers are only now able to offer DDR2 modules with sufficiently high speeds so that the platform does not suffer from a slump in performance.
• The integration of the DDR2 memory interface in the CPU was not possible earlier due to costs or capacity bottlenecks.

What Does DDR2 Memory Offer?

In purely theoretical terms, the memory bandwidth of the available DDR2 modules is up to double that possible with regular DDR (now sometimes called DDR1). The DDR-400 module on Socket 939 processors, for instance, managed a theoretical 6.4 GB/sec. An AM2 processor with its DDR2 memory interface and a 400 MHz module (DDR2-800) should be able to hit a theoretical 12.8 GB/sec.

Overview of theoretically possible memory bandwidths of DDR and DDR2 memory at various speeds

If we compare the theoretical values with those achieved in practice, however, the old Socket 939 with DDR1 looks fantastic. At 6.2 GB/sec, the integrated memory interface was able to attain up to 97% of the theoretically possible bandwidth with the DDR1 memory modules. As we began testing, we assumed that if the new DDR2 memory interface even approached this efficiency level, the new processors using the AM2 socket would really take off.