We proceed with the low-level analysis of the most important characteristics of high-performance DDR2 memory modules using our RightMark Memory Analyzer test package, started by our previous article devoted to Kingston DDR2-750. In this article we shall review Corsair modules of the traditional XMS2 series, intended for 333 MHz (DDR2-667, to be more exact, DDR2-675, as the manufacturer calls them). On the face of it, they are no different from the XMS2-5400C4 modules reviewed long ago, but this impression is misleading. The point is that the given modules can operate with the lowest 3-3-2-8 timings - not at 266 MHz, as you may expect, but in DDR2-667 mode.
Module manufacturer: Corsair Memory
Photo of the memory module
Module Part Number
The manufacturer's web site does not publish the DDR2 Part Number expansion of XMS2-series memory modules. The datasheet runs that the product under review is a set of two DDR2-667 512 MB modules, based on 64M x8 chips. 100% stable operation is guaranteed in DDR2-675 mode with Intel chipsets and 3-3-2-8 timings, which requires significantly higher voltage than normal — 2.1V. SPD timings are much higher — 4-4-4-15.
SPD chip data
Description of the general SPD standard:
Description of the specific SPD standard for DDR2:
SPD contents are not quite typical of a DDR2-667 module. There is only one CAS# latency value supported — 4, it corresponds to the 3.0 ns cycle time (333.3 MHz, DDR2-667). The timings scheme for this (only) case is 4-4-4-15, as specified by the manufacturer in the documentation. Another distinctive feature is a slightly increased minimum refresh to active/refresh command period (tRFC = 105 ns). But nevertheless, it can be found in other high-performance DDR2 modules as well. Besides, there is no data on a manufacturing date and a serial number of these modules — it actually looks strange for a high-end brand memory module.
Testbed Configurations and Software
Pay your attention: we used 200 MHz FSB in all cases — in nominal DDR2-667 mode (Testbeds 1-4) as well as in overclocked DDR2-800 mode (Testbeds 5-6). The reason is as follows: none of the motherboards is capable of operating at 266 MHz FSB in these modes (DDR2-667/800), not only with these Corsair memory modules. Here emerges the reasonable question as to why test the memory in DDR2-800 mode? The answer to it is the fact that the modules under review are quite robust — due to significantly increased voltage (2.1V) as well as excellent timing characteristics of the memory chips (unfortunately we didn't manage to make out any meaningful designation to determine their manufacturer and technical characteristics).
In the first series of tests we used the timing scheme, set in BIOS Setup by default (Memory Timings: "by SPD"). As you can see, the motherboards that took part in our tests (Testbeds 1-4) obviously didn't agree on the default values — despite the correctly written SPD data exactly for this case (DDR2-667). Most of them set the 4-4-4 (-12/15) scheme, while ASUS P5WD2 Premium (Testbed 3) preferred more conservative 5-5-5-15 timings. Paradoxical, but true: this motherboard uses lower 4-4-4-15 timings for these modules in DDR2-800 mode, while Gigabyte 8I955X Royal on the same Intel 955X chipset, on the contrary, sets the slowest 5-6-6-18 scheme.
So, the best result among DDR2-667 tests is demonstrated (strange as it my seem - higher timings) by ASUS P5WD2 Premium (Testbed 3). It's followed by the second motherboard on Intel 955X — Gigabyte 8I955X Royal. Foxconn products on i945G/P chipsets (which are as slow compared to i955X as 915 chipsets compared to 925 chipsets) bring up the rear. In fact, Foxconn products have never been notable for high memory efficiency.
DDR2-800 mode is completely justified: the modules operate very well in this mode, demonstrating nearly identical data exchange rate with the CPU (it's not surprising — the FSB throughput in this case is just 6.4 GB/s, while the real DDR2-800 potential is twice as high) at somewhat (just a little) lower latencies. There is no absolute leader in this case — ASUS P5WD2 Premium (Testbed 5) still leads in the majority of aspects, while the best random access latency (both with and without hardware prefetch) is demonstrated by Gigabyte 8I955X Royal (Testbed 6).
Timing values, except for tCL, were adjusted "on the fly" due to the built-in RMMA feature that allows to change dynamically memory settings supported by the chipset. Memory operating stability was evaluated with an auxiliary utility RightMark Memory Stability Test, included into RMMA.
Minimal timings allowed by the memory modules under review depend on a given motherboard (to be more exact, on what maximum voltage the motherboard can apply to the memory modules) as well as on a memory operating mode (quite naturally). Foxconn products can apply only 1.9-1.95V to memory modules, thus they do not allow to squeeze maximum from the modules. But at the same time, the result is not that bad — minimal timings are 4-2-2 (we again omit tRAS, as it's ignored by these modules as well as by the majority of other modules). Nevertheless, ASUS and Gigabyte motherboards on the 955 chipset, capable of applying the necessary voltage (2.1V), allow the lowest timings (they cannot be any lower) — 3-2-2 — lower than 3-3-2(-8), guaranteed by the manufacturer for stable operation. Thus, Corsair modules break another timings record — the previous record, 3-2-2 in DDR2-533 mode, had been achieved by XMS2 PRO-5400C4.
Minimal timings in DDR2-800 mode are also very good — 4-3-2 on both motherboards from ASUS and Gigabyte (remember that nominal timings for "typical" DDR2 modules are the following: 3-3-3-9 for DDR2-400, 4-4-4-12 for DDR2-533, 5-5-5-15 for DDR2-667, they must be still higher for DDR2-800 — about 6-6-6-18).
What concerns performance of these modules under "extreme" conditions — ASUS P5WD2 Premium (Testbed 3) in DDR2-667 mode retains its leadership. But in case of DDR2-800 tests, we have a different leader almost in all aspects — Gigabyte 8I955X Royal (Testbed 6), which was outperformed in the previous series of tests, probably due to higher nominal timings 5-6-6-18.
The Corsair XMS2-5400UL modules are well compatible with the motherboards reviewed on Intel 945 and 955 chipsets, they offer good performance as well as huge overclocking potential both in terms of frequency and timings: the modules are stable in their standard DDR2-667 mode with 3-2-2 timings (the absolute record!) as well as in DDR2-800 mode with 4-3-2 timings (which is also an absolute record so far, as we have never carried out our tests in DDR2-800 mode before).
Corsair XMS2-5400UL modules are kindly provided
by Corsair Memory representative office in Russia
Dmitri Besedin (firstname.lastname@example.org)
September 8, 2005.
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