We proceed with the low-level analysis of the most important characteristics of high-performance DDR2 memory modules using our RightMark Memory Analyzer. Corsair XMS2-5400UL modules have recently broken another record, to be more exact — two records: in timings, 3-2-2 in DDR2-667 mode, as well as in performance — these are the first modules tested in DDR2-800(!) mode. Besides, they demonstrated an excellent timing overclocking potential for this case — 4-3-2. In today's article we shall review another offer from Corsair, again from the XMS2 series — not DDR2-800, as you might have expected, but the 500(!) MHz modules, that is capable of DDR2-1000 mode (even if it's not the official specification, approved by JEDEC).
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. The manufacturer guarantees 100% stable operation in DDR2-1000 module with high-performance motherboards, 5-4-4-9 timings, and 2.2V voltage (higher than the nominal voltage by 0.4V, i.e. by nearly 25%). According to the manufacturer, the timings, written in SPD, are also 5-4-4-9.
SPD chip data
Description of the general SPD standard:
Description of the specific SPD standard for DDR2:
The SPD contents look utterly non-standard as well as the DDR2-1000 mode. First of all, according to the SPD, the maximum mode is DDR2-800, not DDR2-1000. This mode corresponds to the first of the supported values tCL = 5. The full timing scheme can be written as 5-5-5-18 — it's far from the official 5-4-4-9, admit it, especially in DDR2-1000 mode. It's not clear what to make out of the second reduced tCL = 4. It corresponds to the 3.7 ns cycle time, which corresponds to 270 MHz — i.e. sort of the DDR2-540 mode. I have absolutely no idea about the reasons. Of course, the non-standard cycle time resulted in the main timing values presented by rational quantities — which can be rounded to 4-3.4-3.4-12.2 in the best scenario. In the worst case (that's what the majority of motherboards are likely to do) — to 4-4-4-12. Like XMS2-5400UL, these modules lack information on the manufacturing date and the serial number — not quite a good thing for brand high-end modules.
Testbed Configurations and Software
There are only few motherboards taking part in out tests — to be more exact, just two models: ASUS P5WD2 Premium and Gigabyte 8I955X Royal. That's because few models allow the Memory/FSB frequency divider = 2.0 as well as to apply relatively high voltage (2.2 V) to memory modules.
We tested our modules on these motherboards in two modes — DDR2-800 with the standard 200-MHz FSB and DDR2-1000, which required the non-standard 250 MHz FSB. Besides, in each case we tested efficiency of the memory system, both single-channel and dual-channel options. The single-channel tests are necessary, because it's impossible to reveal the full potential of DDR2-800 modules in dual-channel mode with the currently available FSB frequencies. Indeed, the peak memory bandwidth of the dual-channel DDR2-800 (12.8 GB/s) is twice as high as the peak bandwidth of the 200 MHz FSB (6.4 GB/s); and the dual-channel DDR2-1000 memory bandwidth (16.0 GB/s) is twice as high as the bandwidth of the 250 MHz FSB (8.0 GB/s). But the single-channel mode allows to even the peak bandwidths of the FSB and memory.
As usual, memory timings were set by default (BIOS Setup — Memory Timings: "by SPD"). As you can see, the ASUS and Gigabyte motherboards do not agree on the standard values for the DDR2-800 mode (the 5-5-5-18 timings are written in SPD for this very mode). ASUS sets the maximum 5-6-6-18 scheme and Gigabyte — the faster 5-5-5-15 scheme, resulting in reduced memory access latencies.
Performance results of the modules in dual-channel and single-channel modes are practically the same (somewhat increased maximum real memory bandwidth, obviously exceeding the theoretical limit, has to do with a relatively L2 Cache in a CPU). It means that the modules under review (actually like the other DDR2 modules) are really capable of the memory bandwidth, close to the theoretical limit. It does not come due to the dual-channel mode. Interestingly, pseudo-random and random memory access latencies in dual-channel mode are practically comparable to those in the single-channel mode. They are even a tad lower in some cases.
What concerns the DDR2-1000 mode — alas, there is only one contender here — the ASUS P5WD2 Premium motherboard. The second contender — Gigabyte 8I955X Royal — failed to start up in this mode despite all our efforts (such as applying higher voltage (2.3V) and manually assigning maximum timings). The default timing scheme for this mode on the ASUS motherboard is the same — 5-6-6-18.
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.
Minimum timings, allowed by these memory modules in DDR2-800 mode without losing stability, turned out the same on both motherboards — 4-3-3 (we again "forget" about tRAS, as it's ignored by these modules as well as by the majority of other modules). Unfortunately, lowing down timings to 4-3-2 (this very record was achieved by Corsair XMS2-5400UL modules in our previous review) resulted in errors.
The minimum stable timings scheme for the DDR2-1000 mode is 5-3-3 — we managed to set this mode only on the ASUS P5WD2 Premium motherboard. Good news: this scheme is noticeably lower than the official scheme for this mode — 5-4-4-9. As we haven't carried out memory tests in the non-standard DDR2-1000 mode before, we have here another record achieved by Corsair modules.
The reviewed Corsair XMS2-8000UL memory modules proved themselves as high-performance modules, which can fully reveal the potential of this memory type in the standard DDR2-800 mode as well as in the non-standard DDR2-1000. It's too early to speak of their compatibility with various motherboards, as there are currently only two motherboards supporting such high-performance memory modes. Nevertheless, even in this case the DDR2-1000 mode is available only in one of them — ASUS P5WD2 Premium. It means that such high-performance non-standard solutions are evidently too buggy (it's hard to tell why the modules don't work with Gigabyte 8I955X — whether it's the fault of the modules themselves, the motherboard, the chipset, or the BIOS version). On the other hand, it's hard to imagine real users of high-performance modules (even DDR2-800), considering the 200 MHz and rarely 266 MHz FSB and plenty of dual-channel DDR2-533. So, high-performance modules are interesting as technological innovations rather than mass products. So in conclusion, let's dwell on the technical aspect of our review, overclocking potential of the modules (timings) in particular. This potential is quite good — the modules can operate stably in DDR2-800 mode with 4-3-3 timings (a tad worse than the previous record 4-3-2, achieved by slower Corsair XMS2-5400UL modules, strange as it may seem); in the standard DDR2-1000 mode — with 5-3-3 timings (it's still the absolute record, as we haven't tested DDR2-1000 before).
Corsair XMS2-8000UL modules are kindly provided
by Corsair Memory representative office in Russia
Dmitri Besedin (firstname.lastname@example.org)
September 29, 2005.
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