Memory manufacturers might not want you to know but the upgrade market for fast DDR memory is as dead as a dead thing. According to the legendary Steampowered survey AMD processors around the 2GHz mark are still very popular so the odds are we're talking about Socket 939 Athlon 64 X2 with a rating of 3800+ or 4000+. If that's your processor of choice then we wish you well but all you need is 2GB of PC3200 for £70 and you'll be a happy camper but it doesn't much matter which memory you choose so long as it's reliable.
At the other end of the scale we've got DDR3, which is horribly expensive at £250-£400 for 2GB.
As we saw in our memory round-up the price of DDR3 is scary but the real problem is that it currently doesn't deliver a significant increase in performance over DDR2.
Slap bang in the middle of the memory market we've got DDR2, which caters for Socket AM2 Athlon 64 and the vast bulk of recent Intel chipsets and motherboards. It's essential that your memory can run at the same speed as the front-side bus (FSB) or it will act as a severe bottleneck in performance so you might think that you need staggeringly fast memory to be compatible with your 1,066MHz or 1,333MHz FSB Core 2 Duo.
In fact you don't.
A 1,066MHz Kentsfield runs on a quad-pumped 266MHz FSB so you only need memory with a true speed of 266MHz, which is an effective DDR speed of 533MHz. Just to complicate things DDR2-533 is often referred to as PC2-4200.
In the case of a 1,333MHz FSB you need PC2-5300, aka DDR2-667, but if you take a look at the websites of the various memory manufacturers and overclocking stores you'll get the impression that their shelves are groaning with memory that runs beyond the 1,100MHz mark, which puts us firmly in to overclocking territory.
This 2x1GB kit of Crucial Ballistix Tracer PC2-8500 memory that I'm looking at today has a rated speed of 1,066MHz so it supports a FSB of 533MHz. That's significantly faster than the 450MHz FSB we have personally seen on a Core 2 Duo using a stock multiplier and everyday cooling and voltages but once you hit the limits of the FSB you can crank up the memory multiplier so that nothing goes to waste.
The timing figures of the Ballistix are 5-5-5-15, which is in line with competing PC2-8500.However, the price is £10 or £20 lower than you might expect for branded first-on-first memory. No doubt this is helped by the fact that Crucial is a division of Micron, which is a manufacturer of memory chips as that must surely keep costs down.