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 nsFSB800 (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 nsFSB800 (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).
