In Search of True DDR2 Bleeding Edge Memory

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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