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.