the support of dual-channel memory access, the AMD engineers improved the memory controller of Socket 939 CPUs for better compatibility with different memory modules. They introduced a special 2T DRAM Timing, which lowers the bar the memory controller of the Athlon 64 sets for DDR SDRAM modules. Thanks to that, the Socket 939 Athlon 64 can work with four memory modules in the DDR400 SDRAM mode. You should be aware, though, that the highest performance, with the most aggressive 1T timing, is only achievable when you plug in a couple of identical DDR400 SDRAM modules. When four memory modules are in use, the memory controller of the Athlon 64 can only support DDR400 SDRAM with the slower 2T timing. Moreover, if the four installed modules are two-sided, the speed of the memory subsystem will be dropped to DDR333 even with 2T timing.
