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DDR2 vs. DDR: Was It Worth It?

Before we pass over to the performance tests of the new AMD Socket AM2 platform, we decided to take a closer look at the DDR2 SDRAM and the advantages it should bring to the Athlon 64 platform in terms of performance. It is no secret for anyone here that AMD platforms are very sensitive to the memory subsystem latency. And even though the transition from DDR to DDR2 SDRAM promises a significant increase of the memory bandwidth, it doesn’t really reduce the latencies.

To obtain some practical results that could allows us make some conclusions about the performance improvement from the transition to DDR2 SDRAM, we assembled two identical systems with DDR and DDR2 memory and compared the performance with different memory timings and memory bus frequencies. We used the following CPUs for these tests: Athlon 64 FX-60 for Socket 939 and Athlon 64 FX-62 for Socket AM2 with the core clock dropped down to 2.6GHz. Note that we installed 512MB memory modules for these tests, so the total amount of RAM in the test systems equaled 1GB.

First of all let’s take a look at the synthetic benchmarks results showing memory bandwidth and latency:

The practical results prove our theoretical suppositions. DDR2 SDRAM boasts higher bandwidth than the regular DDR memory, and as the memory frequency increases, so does the bandwidth. However, the situation with latencies is totally different. Only DDR2-800 SDRAM with rather aggressive timings (for this frequency) 4-4-4 can compete with DDR400 SDRAM working with minimal timing settings of 2-2-2. DDR2-667 with the minimum possible timings of 3-3-3 can only reach the same practical latency as DDR400 with 2.5-3-3 timings and cannot compete with fast DDR SDRAM. As for DDR2-533 SDRAM, this memory is definitely worse than any DDR400 SDRAM in terms of latency.

The results of SiSoftware Sandra 2007 correspond to the results we obtained in Sciencemark 2.0. In fact, it is evident already that the performance of your Socket AM2 system will improve only if you have DDR2-800 SDRAM or fast DDR2-667 SDRAM with 3-3-3 timings settings. The performance gain in all other cases is pretty questionable and will primarily depend on the type of applications running.

 
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