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| DFI 855GME-MGF and Intel Pentium M 735 Along came a Dothan | |
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(Review by MS, Jan 2, 2005) |
Memory Bandwidth Performance
In a world dominated by 6GBs memory read bandwidth figures in dual channel configurations, a single channel memory subsystem appears to have a definite handicap. To give some idea of how much bandwidth the 855 GME delivers, we have a few "Everest" benchmark numbers for Read and Write performance. In all cases, the PSB was set to 133 MHz with varying memory to PSB ratios.
Read and Write performance at 1:1 (266 MHz), 5:4 (344 MHz), 5:3 (442MHz) -2.5:3:3:6, 5:3 (442 MHz) - 2:3:2:6
Certainly the memory bandwidth is a far cry from what we are used to see on Pentium4 and Athlon64 platforms but what about latencies?
Memory Subsystem Latency (Cachemem)
We are comparing the P4 Extreme Edition with the Dothan. Both CPUs have approximately 2MB on-die SRAM cache (2.5 MB for the XE) but the organization is very different in that the Extreme Edition features an 8 kB L1 data cache as opposed to the 32 kB L1 data cache of the Dothan. That means that data blocks up to 32 kB can fit into the L1 cache of the Dothan whereas the same data blocks would need to go into the L2 cache of the P4 XE. The difference in terms of access latency is very obvious in the Cachemem plot below where all transfers are still in the 1 ns range in the case of the Dothan (turquois) while in the case of the P4, the same transfers take 3-4 ns. The same differences are found in the L2 vs L3 transfers where the Dothan acts within 6ns (1.6GHz) to 4ns (2.26 GHz) whereas the same transfers take 10 - 20 seconds on the L3 cache of the P4 XE. With respect to main memory latencies, the P4XE does not look too bad but we were running the DDR2 at 3:3:3 which is below the official DDR2 latency specifications.
Memory access latencies of the 925XE with the P4 3.46 (1066 MHz PSB) - transparent blocks - against the 855 with the Dothan Pentium M 735 at 1.6 GHz (12 x 133 MHz / 533 MHz PSB) - turquois blocks. At higher multiplier settings, the L2 latencies are even shorter because of the higher clock speed of the CPU.
The P4 system is running at 3:3:3:8 latency settings, the Pentium M is running at 2:3:3:6 (CAS: tRCD: tRP: tRAS)
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Pentium M 735 (Dothan 1.7 GHz) |
next page: => Application Performance: WorldBench5 =>
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