Is it DDR3 time, yet?

When a new memory type arrives, there is always controversy over whether it is actually any faster than what it is supposed to replace. Sometimes, the controversy continues long enough to end the new RAM's hopes of dominance - as in the case of RAMBUS.

But after a while, the inflated price at introduction drops, speed increases, and the new memory type succeeds the old. Is it now that time for DDR3?

Memory remembered

When DDR2 memory arrived, it really wasn't faster than DDR. In fact, it was slower in lots of tests. This seemed a bit odd, when the bandwidth available appeared to be greater. But that's not the only factor in memory performance. Another important consideration is its timings - represented by those four numbers in the memory specification, like 2-2-2-5 or 7-7-7-18. The first of the quartet is the most significant, as it refers to the CAS Latency.

Although memory throughput is a major contributor to system speed, the time modules take to get up to speed will also have an effect. A longer CAS Latency - represented by a larger timing number - will mean the modules take a few more nanoseconds to deliver their maximum throughput.

So a module with a CAS Latency of 4 theoretically takes half the time to fire up data delivery than one with a CAS Latency of 8 (although all the other timing values means it's really much more complicated than this).

When DDR2 first arrived, it boasted 50 per cent or greater throughput than PC3200 DDR. But it usually had twice the latency to go with it. So, in true swings and roundabouts fashion, it wasn't really any faster.

The problem memory regularly faces is that the speed the DRAM cells can achieve internally reaches a ceiling, which prevents faster modules being created. So each successive generation of DDR adds clock-doubling technology so the cells themselves can actually run slower - and consume less power. The latter will be particularly important as we sit on the cusp of 64-bit operating systems finally becoming the norm, so that more than 4GB of memory are worth having.

We're now on the third clock-doubling generation. Where DDR is 2x SDRAM, DDR2 is 4x, and DDR3 8x. At the same time, voltages have dropped from 2.5/2.6V to 1.8V to 1.5V respectively (and SDRAM operates at 3.3V). But each time, increased latency has had to be introduced to make things work.

Eventually, as the memory technology is improved, the latency is reduced a little whilst the full throughput possibilities are realised. For example, the fastest DDR standard is PC3200, but 1,066MHz DDR2 is PC2-8500 - ie 2.65 times the bandwidth. But the fastest CAS Latencies are 2 and 5 respectively (although 4 is possible at 800MHz). So the extra bandwidth just about outweighs the increased latency.

DDR3 versus DDR2

The question is, now that Nvidia has come out with chipsets supporting DDR3, and Intel has had them for over a year, is this happening to DDR3 yet? So I thought I'd do a little spot testing of my own to see how DDR3 is faring. Helpfully, MSI makes a motherboard which accommodates either DDR3 or DDR2. And it's not based on some reduced entry-level chipset, either. The X48c Platinum uses Intel's latest X48 chipset, so will even support 1,600MHz FSB processors.

I put together a PC with an Intel Core 2 Extreme QX9650 and BFG Technology NVIDIA GeForce 8800GTS 512MB graphics. Using two 1GB sticks of Crucial Ballistix DDR2 PC2-6400 running at 800MHz with 5-5-5-18 timings, the PC achieved 13,650 3DMarks in Futuremark's 3DMark06 v110.

Using two 1GB sticks of Corsair TwinX DDR3 PC3-10,600 running at 1,333MHz with 9-9-9-24 timings, the PC achieved 13,749 3DMarks. So that's 0.7 per cent extra performance.

Bearing in mind that the DDR2 costs around £40 and the DDR3 more like £70, you're paying 75 per cent more for 0.7 per cent extra speed. From this rather unscientific single test, it would appear DDR3 still isn't very good value.

Thank heavens at least MSI has had enough sense to release a motherboard where you can still enjoy the low cost of DDR2 still whilst reaping the benefits of the fastest Intel processors this year. Then you can move over to DDR3 when it really does make a difference.

But in the long run, the lack of difference between DDR2 and DDR3 will be a moot point, since performance features and overclocking enhancements like XMP will increasingly only be available with the premium chipsets, which will primarily be focused on DDR3. So even if the performance benefits aren't really that significant, we'll all have to move over to DDR3 soon anyway.