Boosting Memory Clock Speed: 23% Performance Gains
Boosting Memory Clock Speed: 23% Performance Gains
On the other hand, boosting memory clock rate by itself can produce significant performance gains. As before, we used the outstanding Corsair CM2X512-8000UL Corsair memory modules for the memory clock speed and latency analysis below.
The clock rates for DDR2-400 up to DDR2-800 were analyzed in tandem with FSB speeds of 800 and 1066. The reference point for our analysis is DDR2-533 RAM, because this is the type most frequently-installed in commercial PCs. That's because DDR2-400 is neither very prevalent nor very widely used.
Speed analysis with an FSB speed of 800:
| Module Clock Speed (CL 5.0-5-5-15) FSB800 (200 MHz) | |||
|---|---|---|---|
| FSB800 (200 MHz) | Read | Write | Latency |
| DDR2-800 (400 MHz) | 6189 MB/sec | 2142 MB/sec | 82.9 ns |
| DDR2-667 (333 MHz) | 6105 MB/sec | 1985 MB/sec | 88.0 ns |
| DDR2-600 (300 MHz) | 6052 MB/sec | 1890 MB/sec | 88.1 ns |
| DDR2-533 (266 MHz) | 6024 MB/sec | 1743 MB/sec | 89.5 ns |
| DDR2-400 (200 MHz) | 5464 MB/sec | 1389 MB/sec | 111.4 ns |
| FSB800 (200 MHz) | Read | Write | Latency |
| DDR2-800 (400 MHz) | 102.7% | 122.9% | 108.0% |
| DDR2-667 (333 MHz) | 101.3% | 113.9% | 101.7% |
| DDR2-600 (300 MHz) | 100.5% | 108.4% | 101.6% |
| DDR2-533 (266 MHz) | 100.0% | 100.0% | 100.0% |
| DDR2-400 (200 MHz) | 90.7% | 79.7% | 80.3% |
This table shows clearly what we measured in our labs at THG: if a DDR2-800 memory module is used with an FSB speed of 800, it can boost memory read access by 2.7% and write access by 22.9%. The latency timing in our measurement improves by about 8%. From these results we draw the following conclusion: Those who don't boost FSB speeds won't realize any significant performance improvements simply from faster memory clock speeds.
A speed analysis with an FSB speed of 1066:
| Module Clock Speed (CL 5.0-5-5-15) FSB1066 (266 MHz) | |||
|---|---|---|---|
| FSB800 (200 MHz) | Read | Write | Latency |
| DDR2-888 (444 MHz) | 7819 MB/sec | 2554 MB/sec | 73.9 ns |
| DDR2-800 (400 MHz) | 7748 MB/sec | 2431 MB/sec | 75.6 ns |
| DDR2-711 (355 MHz) | 7673 MB/sec | 2258 MB/sec | 76.3 ns |
| DDR2-667 (333 MHz) | 7310 MB/sec | 2110 MB/sec | 83.6 ns |
| DDR2-533 (266 MHz) | 7066 MB/sec | 1822 MB/sec | 86.3 ns |
| DDR2-400 (200 MHz) | 5732 MB/sec | 1458 MB/sec | 105.2 ns |
| FSB800 (200 MHz) | Read | Write | Latency |
| DDR2-888 (444 MHz) | 110.7% | 140.2% | 116.8% |
| DDR2-800 (400 MHz) | 109.7% | 133.4% | 114.2% |
| DDR2-711 (355 MHz) | 108.6% | 123.9% | 113.1% |
| DDR2-667 (333 MHz) | 103.5% | 115.8% | 103.2% |
| DDR2-533 (266 MHz) | 100.0% | 100.0% | 100.0% |
| DDR2-400 (200 MHz) | 81.1% | 80.0% | 82.0% |
This table reflects our test series and documents some impressive results. With an FSB speed of 1066 (266 MHz), a switch to DDR2-888 finally starts to pay off. Read access times then improve by 10.7% and write access times by 40.2%. At 16.2%, the speed boost for latency is double that for an FSB 800 system. This doesn't demonstrate anything startling, however: the bottleneck in a DDR2 Intel platform has been and remains the front side bus (FSB).
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