Memory matters

If you’re confused about memory, look no further. In this article, you won’t find any breathless discussion of the latest memory heatsinks or flashing lights, but you will learn the basics of how a PC’s memory works, why it’s important and how to choose the right memory upgrade for your system.

We’ll concentrate on the ‘need-to-know’ information that will help explain why choosing the right memory for your own PC is so important and, more importantly, why it’s usually a waste of time poring over memory specification sheets to find something faster.

We can’t cover everything about memory here, but if there’s any aspect that still puzzles you, drop us a line (letters@pcw.co.uk) and we’ll do our best to address the issues in future features or in our Hands On Question Time pages.

The internet is awash with hardware review sites that cover memory modules in excruciating detail. Unfortunately, a lot of the information is misleading, out of date or simply irrelevant. So unless you’re designing a system to put on show, should you really care about the colour of the heatsink?

If you do think that the hue of the heatsink is important, then you’re in the wrong place. In an attempt to add some glamour to what is a rather dull but technically complex commodity, memory manufacturers have become expert at adding all manner of ‘features’ that won’t necessarily enhance your PC’s performance but will allow a premium price to be charged for so-called performance memory. It may well be good memory, but you’ll be disappointed if you’re expecting it to work instant wonders.

Back to basics
We’ll start with a simple fact that you rarely see mentioned: whatever the nominal data transfer speed quoted for a memory module, all currently available desktop memory chips operate at an internal frequency of no more than 200MHz, a figure that hasn’t changed for many years (see chart on the attached PDF, Internal speed of memory). Even the latest 1,600MHz modules plod away internally at a speed eight times slower than the advertised rate. How so? Well, it’s all down to some clever internal trickery. For a primer on how memory works, see the 'Refresh your memory' section in this feature.

All PCs and laptops now use DDR SD-Ram (double data rate synchronous dynamic Ram), although older models may still use the single data rate type, usually just called SD-Ram. You might even find a very old PC with asynchronous D-Ram, such as Fast Page Mode (FPM) or Extended Data Out (EDO) D-Ram, although it’s getting harder to buy this type of memory, which comes in Simms (single in-line memory modules) rather than the modern Dimms (dual in-line memory modules).

Synchronous D-Ram is designed to operate at the same speed as the PC’s system bus (the connection between the processor and memory); it’s known as the FSB (front-side bus) speed. So if your system bus runs at 133MHz, the memory clock will also run at 133MHz.