AMD's AM2

[Ruslan74]

Toms Hardware has a nice article on the new flagship from AMD which uses DDR2 RAM and has significant internal changes to the core and memory of the CPU. Nforce 5 chipsets, DDR2 SLI Memory, benchmarks, OpenGl and DX performance, etc.

Its quite a lenghty read so grab a mug of hot chocolate and read away...


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.

[spAc3dd]

Yeah there is a bit of a problem with the DDR2 and the Dual Channel memory controllers built into the CPU. I read that performance is a but iffy in that article.

The Theory:

"AMD decided in favor of the integrated memory interface in the CPU to ensure it can work at full processor speed, and attain a far higher bandwidth than is possible with a Northbridge interface connected via a slow bus. That was the theory anyway. This worked like a dream with Socket 939 and DDR memory; at a CPU clock speed of between 2 GHz (Athlon 64 X2 3200+) and 2.8 GHz (Athlon 64 FX-57), read and write speeds from memory hardly fluctuated at all."

The Reality:

"With the DDR2 memory interface, the reality no longer matches the theory: data transfer rates fluctuate between 6.4 and 8.1 GB/sec when reading, at the same CPU clock speeds as the foregoing DDR1 comparison. The variance is almost 21%.

Only at clock speeds of 2.6 GHz and above does memory interface performance improve. That's because of the poor CAS latency (CL4.0) of DDR2 memory with a high data throughput, compared to DDR1 (CL2.0). Here the Athlon 64 X2 5000+ (2.6 GHz) achieves a value of 7.6 GB/sec, with the Athlon 64 FX-62 at 2.8 GHz scoring a top throughput of 8.1 GB/sec.

When writing, things are even worse: here the performance of CPUs with lower clock speeds really falls apart. With a 2 GHz processor (Athlon 64 X2 3200+) the memory bandwidth is a whopping 200 MHz/sec below the DDR1 value, achieving a paltry 5.6 GB/sec. Only at high clock speeds - 2.4 GHz and above - does performance rise above the values of the old DDR1 memory.

The strong dependence of DDR2 memory on CPU speed represents a huge performance loss for midrange processors when compared against DDR1 versions. This is also reflected in the performance of practical applications."

I would wait a while for this new stuff to sort itself out...

[doobiwan]

From what i can see, the long and the short of it is that unless you can afford the best of everything ddr2-800, 64 x2/FX's it's not worth it, potentially even detrimental to performance.

Thanks, but I'm going to hold out for the Conroe, or hopefully the K8L (Whichever gives me better price/performance)