DDR2 SDRAM for Overclocking Fans: Getting Beyond 1GHz

Using new overclocker-friendly modules of DDR2 SDRAM – Corsair TWIN2X1024A-5400UL, Mushkin XP2-6400 DDR2 and OCZ DDR2 PC2-8000 Platinum Enhanced Latency Dual Channel – we are going to check the performance of Pentium 4 systems with DDR2-1067 and DDR2-800 SDRAM. You will also see how memory frequency and timings affect the overall performance of a Pentium 4 platform.

by Ilya Gavrichenkov
08/22/2005 | 12:54 PM

Not long ago we discussed the new features of the memory controller in Athlon 64 processors of the E revision, among which we noted the unofficial support of memory types faster than DDR400 SDRAM (for details see our article called AMD Athlon 64 Processors on E Core: Memory Controller Peculiarities in Detail . We came to the conclusion then that it was possible to increase somewhat the performance of Athlon 64 systems by using DDR500 SDRAM. Even though this memory is not standardized by JEDEC, SDRAM module makers are offering many such modules to overclockers and PC enthusiasts.

 

But AMD is not alone in its supporting, even though unofficially, overclocker-friendly memory modules. Intel follows a similar policy with respect to DDR2 SDRAM: Intel’s new i955X and i945P chipsets formally support memory no faster than DDR2-667 SDRAM, but unofficially they can work with much faster modules.

Thanks to this feature of the new chipsets from Intel, overclocker-friendly modules of DDR2 SDRAM available from such manufacturers as Corsair, OCZ and others, may become very popular among PC enthusiasts. But first we must of course evaluate the performance gains we can expect to get with such memory in comparison with the “ordinary” performance of platforms that use standard DDR2 SDRAM.

In this review you will see a few overclocker-friendly modules of DDR2 capable of working at high frequencies as well as at extremely low timings. We will also use them to check if high-frequency DDR2 SDRAM brings any real gains to modern Pentium 4 systems and if it makes sense to keep the memory timings as low as 3-2-2-8.

We should acknowledge as a fact that DDR2 SDRAM isn’t widely accepted as yet. For example, the usage statistics for CPU-Z, a popular tool in the overclocking community, says that DDR2 SDRAM is installed only in 4.2% of all systems this program is launched on. Such a low popularity of this memory type is not to be wondered at just because it hasn’t had any obvious advantages against DDR SDRAM until recently. The next year is going to be a breakthrough for DDR2, however. DDR2-800 SDRAM modules are expected to appear in mass quantities in 2006 and this kind of memory seems to ensure tangible performance advantages in comparison with DDR400 SDRAM. Considering other appealing traits of DDR2 technology like low power consumption and simplified mainboard wiring, this memory type will most likely shatter the market position of DDR1.

A new family of Athlon 64 CPUs intended for the new M2 socket will soon make another favorable factor for DDR2 SDRAM, too. These processors are scheduled to appear in the second quarter of 2006 and will support 667MHz and 800MHz DDR2 SDRAM instead of DDR1 SDRAM. So, our exploration of characteristics of high-speed DDR2 memory modules may be also interesting for people who use the K8 platform, since it is going to add DDR2 support quite soon.

Now that we’ve made sure about the bright perspectives of DDR2 SDRAM, we can examine the products about to be tested.

DDR2 Memory Modules for Overclockers

Corsair TWIN2X1024A-5400UL

Corsair has sent us their TWIN2X1024A-5400UL memory kit that consists of two identical 512MB DIMM modules intended for use in dual-channel configurations. Although TWIN2X1024A-5400UL modules undergo compatibility tests before reaching shops, Corsair specifically mentions that this memory is recommended for use in mainboards based on NVIDIA’s nForce4 SLI Intel Edition chipset. This is more of a marketing statement, though. At least, we had no troubles with this kit when we installed it into mainboards based on Intel’s chipsets.

According to Corsair, TWIN2X1024A-5400UL modules are one of the best DDR2 SDRAM offerings from the company. This memory is tested for operability at 675MHz frequency and with 3-3-2-8 latencies. Note that these characteristics apply only to version 1.2 TWIN2X1024A-5400UL kits (the version number is indicated on the module’s sticker). For earlier versions of its DIMM kits the manufacturer guaranteed more aggressive timings (3-2-2-8), but later they decided to worsen the characteristics a little to reduce the manufacturing cost.

The modules from the kit look quite typically for Corsair’s produce. They are covered with aluminum heatsinks painted glossy black. A sticker with an XMS2 series logo is on one side of the module, and a sticker with the marking is on another. The latter sticker among other things tells you the frequency and capacity of the module.

So, here is the official specification of the Corsair TWIN2X1024A-5400UL memory modules:

Note that the standard voltage of DDR2 SDRAM is 1.8V, but Corsair declares 2.1V for these modules. So, if you want to use your TWIN2X1024A-5400UL kit in the specified mode, make sure first your mainboards supports this voltage, too.

The information from the module’s SPD differs from the specification somewhat:

As you see, the SPD latencies are less aggressive than those from the specification. This discrepancy is due to Corsair’s trying to ensure maximum compatibility of its modules with various platforms. For TWIN2X1024A-5400UL modules to work in all configurations and at 1.8V voltage, less strict settings are written into their SPD.

Our tests proved that Corsair’s TWIN2X1024A-5400UL modules are kind of universal. That is, they can work at 675MHz with extremely low timings but can also work at a much higher frequency if the latencies are increased a little.

Mushkin XP2-6400 DDR2

We have never reviewed PC memory from Mushkin on our site but it doesn’t mean the company is new to the SDRAM market. Mushkin was founded in 1994 as a subsidiary of Ramtron International Corp., the name that is now closely associated with ferroelectric memory (FRAM). Mushkin has nothing to do with FRAM, however, but has been supplying modules of ordinary SDRAM for all these years.

Mushkin offered us their XP2-6400 modules. These modules are currently the company’s fastest DDR2 product and are rated to work at 800MHz frequency with rather aggressive 5-3-3-8 timings.

Mushkin doesn’t make any “best in the world” statements about its products and the modules look rather plain externally. The Mushkin XP2-6400 DDR2 kit is a pair of identical DIMM modules equipped with heat-spreaders made of anodized aluminum of a matte black color. The company’s name and the words “Enhanced Memory” are extruded on the heat-spreaders. The marking and the timings of the memory can be read on the stickers.

The official specification of the Mushkin XP2-6400 DDR2 kit follows below:

Note that unlike Corsair’s modules, the XP2-6400 DDR2 kit doesn’t require high voltage to show their best characteristics. The declared frequencies and latencies are achievable at 1.9V already which you can select on almost any LGA775 mainboard available. Mushkin also guarantees the modules to work at 2.1V voltage, which will surely help at overclocking.

The modules’ SPD is programmed like that:

As you see, Mushkin didn’t write into SPD the declared parameters, either. For better compatibility with mainboards these modules contain two sets of parameters in their SPD: DDR2-400 SDRAM with 3-3-3-9 timings and DDR2-667 with 4-5-5-15 timings. Thanks to this setup, you can easily start up any mainboard with XP2-6400 DDR2 modules installed at the default memory settings and then adjust these settings as necessary. Our experience with this kit suggests that this memory is more inclined to work at high frequencies rather than at aggressive timings. We should keep this fact in mind.

OCZ DDR2 PC2-8000 Platinum Enhanced Latency Dual Channel

These modules from OCZ are proudly described by the manufacturer as “the fastest DDR2 memory available today”. We’ll see during our tests if this claim is true, but the modules do look impressive.

This memory kit also consists of two 512MB modules which are equipped with platinum-sputtered copper heat-spreaders, polished to a mirror shine. An embossed logotype of the manufacturer is glued to each module. The mirror-like surface looks cool, but you should be aware that it can quickly get dirty under your fingers.

OCZ claims these modules support 1000MHz frequency at 5-5-5-15 latencies. In other words, this memory evidently aims at conquering high frequencies rather than at keeping the timings low.

Here’s the official specification of the OCZ DDR2 PC2-8000 Platinum Enhanced Latency Dual Channel kit:

So, the specification of this memory kit differs from the competing products in declaring a higher operational frequency but worse timings. The voltage is supposed to be set to 2.1V, like with the Corsair memory, and this may affect the compatibility of this kit (in terms of achieving the specified characteristics) with mainboards that don’t offer much flexibility in controlling the voltage on the DIMM slots.

The OCZ kit features two exclusive technologies: Enhanced Latency (EL) DDR means a special design for stable operation at low latencies and Extended Voltage Protection allows safely using the modules at a voltage below 2.2V without losing the manufacturer’s warranty.

Here’s the SPD information for these modules:

As you see, the OCZ engineers just copied the information from the specification into the modules’ SPD and it may actually get you into trouble. Not all mainboards can correctly interpret the 1000MHz frequency which is written into the SPD unit of these modules. For example, we had problems trying to launch our ASUS P5ND2-SLI Deluxe mainboard, based on NVIDIA’s nForce4 SLI Intel Edition chipset, with the OCZ sticks plugged in. The mainboard would only launch with these modules after you have manually selected the necessary frequency and timings of the memory. And it means you need another pair of DIMM modules to launch the mainboard and adjust the settings accordingly.

As for the practical qualities of the OCZ DDR2 PC2-8000 Platinum Enhanced Latency Dual Channel kit, they proved to be much alike to those of Corsair’s TWIN2X1024A-5400UL. Modules from both kits are actually based on chips from Micron and behave similarly in practice.

Testbed and Methods

So, we’ve got three overclocker-friendly kits of DDR2 memory at our disposal and despite them having different characteristics their manufacturers each claim its particular product to be the optimal choice. To compare them justly, we will test them to find what frequencies and at what timings these memory kits support.

We assembled the following testbed:

Mainboard’s BIOS settings:

Most of the tests were performed at 2.1V memory voltage. This is the voltage all the tested modules are rated for.

Stability Tests

We verified stability of operation in two steps. First, we used the Memtest86+ utility to make sure there were no errors at work. Then we reconfirmed this result by running Windows-based S&M and Prime95 utilities. This two-step approach ensures that we get trustworthy results.

Now let’s get closer to the actual results. The diagrams below show the maximum frequency the memory modules were stable at (as confirmed according to the above-mentioned method) with the given timings.

The first thing you can notice here is that top-end modules of DDR2 SDRAM from different manufacturers do not differ much. It is especially clear with the memory kits from Corsair and OCZ which have almost the same maximum frequencies at different latencies. It’s only at low timings that the OCZ DDR2 PC2-8000 Platinum Enhanced Latency Dual Channel can work at a few megahertz higher frequency than Corsair’s TWIN2X1024A-5400UL. When less aggressive timings are selected, the memory from Corsair and OCZ behaves identically. For example, neither module can conquer 1000MHz frequency even though this frequency at 5-5-5-15 timings is declared to be the default mode of operation for the OCZ kit.

The memory from Mushkin behaves somewhat differently from the other two kits. It is a little worse at aggressive timings. For example, the XP2-6400 DDR2 modules are not stable even as DDR2-667 at 3-3-2-8 or 3-3-3-10 timings. On the other hand, the Mushkin memory accelerates at high timings and notches a better result than the competitors at 5-5-5-15 (by 4MHz only, so this is not a very convincing victory).

To check how the voltage of the memory may affect its overclockability, we tried to give the modules 2.3 volts (this is the maximum the ASUS P5WD2 Premium mainboard can give out) at 5-5-5-15 timings and see what could be achieved. Our modules reacted quite positively to the higher voltage, allowing to raise the “stability bar” more. To be exact, the maximum frequencies at 5-5-5-15 timings and 2.3V voltage were:

Corsair TWIN2X1024A-5400UL

1044 MHz

Mushkin XP2-6400 DDR2

1048 MHz

OCZ DDR2 PC2-8000 Platinum Enhanced Latency Dual Channel

1036 MHz

In other words, our increasing the voltage by 0.2V improved the frequency potential of all the participating modules by about 6% and made it possible to overcome the meaningful barrier of 1 gigahertz.

So, we can say that PC enthusiasts now have much flexibility in configuring the memory subsystem of their LGA775 platforms. Like with DDR1 SDRAM, it is possible either to increase the frequency or reduce the latencies of the memory. Which method is more profitable? We’ll answer this question in the next section of the review.

Latency vs. Frequency: Choosing Optimal DDR2 SDRAM

An improved memory controller is one of the main defining traits of the i955X and i945P chipsets. The controller officially supports DDR2-667 SDRAM, but also brings new divisors for the memory frequency, two of which set up 667MHz frequency at 800MHz and 1066MHz FSB. Besides them, the new chipsets have acquired another important divisor, 1:1. Thanks to this divisor, i955X/i945P-based mainboards can support DDR2-800 SDRAM at 800MHz FSB and DDR2-1067 SDRAM at 1066MHz FSB. The problem is what’s better for a Pentium 4 system, a high memory frequency or low memory timings? As you have seen above, modern DDR2 modules can work as DDR2-667 SDRAM at aggressive 3-2-2-8 timings or easily reach frequencies like 1GHz at 5-5-5-15.

To answer this question we performed a series of tests using DDR2 memory with different frequencies and timings on the same platform. The platform was configured like follows:

The processor we use is an engineering sample so we can freely change its frequency multiplier from 14x to 19x. Thus, we have an opportunity to compare systems that differ not only in their memory subsystems but also in their FSB frequency.

First we set the FSB frequency to 1067MHz. This frequency is often used not only on computers with a Pentium 4 Extreme Edition, but also in overclocked systems based on junior Pentium 4 models. The CPU clock rate was set as 14 x 266MHz = 3724MHz.

In this case the i955/i945 chipsets allow using DDR2-533, 667, 800 or 1067 SDRAM.

Next we set the FSB frequency to near 800MHz. Since we were going to compare the results of the tests, we decided to use an 18x multiplier and raise the FSB frequency a little above the standard value, so that the resulting frequency of the CPU was close to 3.73GHz. Thus, the CPU clock rate was set as 18 x 207MHz = 3726MHz.

When using 800MHz FSB frequency, the i955/i945 chipsets allow setting the memory mode as DDR2-533, 667 or 800 SDRAM. But since we had increased the FSB frequency above the standard, the system clocked the memory as DDR2-552/690/828 SDRAM.

There’s another thing concerning the conditions of our tests that we should mention. As we showed in the previous section, even the most advanced memory cannot boast absolute stability at 1066MHz. Still we attempted to run our tests at this frequency, too, and we were successful with Corsair’s TWIN2X1024A-5400UL sticks. After increasing their voltage to 2.3V and providing additional cooling, we performed our typical tests not only at 5-5-5-15 but also at 5-3-3-15 timings.

Yet we do not claim the system was absolutely stable at such settings, even though it passed our tests. The results of DDR2-1067 are not currently of much practical use since you need to take special measures like increasing the voltage and providing more cooling to assemble a stable computer with a memory subsystem like that. On the other hand, technologies improving, we will surely see mass-produced overclocker-friendly DDR2-1067 SDRAM modules soon.

The final preliminary remark is that not all i955/i945-based mainboards support the 1:1 memory divisor. So, you have to be careful about your choice of the mainboard, not only of the memory modules, in order to build an advanced computer with high-speed memory.

That said, we can at last get to our tests. First, here are some tests that measure the effective bandwidth and latency of the memory subsystem.

As you can see, timings and frequency affect the real performance of DDR2 SDRAM quite heavily. Note that this is conspicuous even despite the limited bandwidth of the processor bus which is no higher than the bandwidth of DDR2-533 SDRAM with Pentium 4 systems.

Obviously, the effect of high-speed memory types should be felt in real-life applications and benchmarks, too.

We can see that the selected timings and frequency of the memory subsystem may have a big effect on the performance of a Pentium 4 system in real applications, too. The FSB frequency also affects the performance quite much. Thus, if you want to squeeze the maximum from your computer, you shouldn’t forget about a proper memory setup besides overclocking the CPU and graphics card.

Memory timings are the performance-determining factor with Athlon 64 systems, but they are not with Pentium 4 platforms. All of our tests indicate that systems with high-frequency memory deliver the maximum performance. This is especially conspicuous when the FSB is clocked at 1067MHz: the systems with DDR2-1067 and DDR2-800 SDRAM are always faster than the systems with DDR2-667 and DDR2-533 SDRAM irrespective of the selected timings.

It’s all the same with an 800MHz FSB, even though DDR2-667 SDRAM with extremely low timings like 3-2-2-8 is just a little faster than DDR2-800 SDRAM with 5-5-5-15 timings. Still, this cannot change the overall picture: memory frequency has a bigger effect on performance than latency when it comes to Pentium 4 systems with DDR2 SDRAM. If you’ve got memory capable of working at 800MHz and higher, you are guaranteed to have more performance than with DDR2-667 or DDR2-533 whatever timings the latter may have. Thus, we fully agree with the manufacturers’ course towards higher frequencies of DDR2 SDRAM they produce.

Conclusion

We used to say that DDR2 SDRAM had no advantages over DDR SDRAM, but it is different now. The design of memory chips makes it easier to increase the frequency of DDR2 than it was with DDR1 and the performance of DDR2 systems improves as the result of the frequency of overclocker-friendly DDR2 SDRAM having grown up to 1 gigahertz. That’s why we are absolutely sure today that the transition to DDR2 SDRAM does make sense.

Today the best choice for PC enthusiasts and overclockers that stick to the Pentium platform is Intel’s new i955 and i945 chipsets as well as NVIDIA’s nForce4 SLI Intel Edition. These chipsets are all capable of working with high-speed DDR2 SDRAM.

In the AMD camp, DDR2-supporting systems for the Athlon 64 are expected to emerge in the second quarter of the next year. We can hope for a certain performance growth with these systems, too, due to the transition to the more progressive memory types.

As for supply, the manufacturers of overclocker-friendly DDR SDRAM modules are steadily mastering the production of DDR2 SDRAM with high frequencies and low timings. The leading companies like Corsair, Mushkin and OCZ already offer modules with impressive characteristics.

So, even though DDR2 SDRAM hasn’t become widely popular in the first year of its being on the market, it is going to rule it in the future. We have no doubt about that.