Apple made the Intel iMac Core Duo a fairly impregnable machine. You can't change any of the hardware components without voiding your warranty; in fact you can't really access anything without a chisel and some wayward behaviour.

The one Achilles heel is the RAM. When you buy either of the Intel iMac Core Duos you get the choice of upgrading from the standard 512MB RAM up to a maximum of 2GB, and for the improvement Apple charges $100 (£57) for a 512MB stick and $200 (£114) for a 1GB stick.

But considering how easy it is to change RAM - about as tricky as changing the fuse on a plug - you can also buy RAM direct from a supplier such as Crucial and save some money by slotting it in yourself. This equates to a £12 saving on a 512MB stick.

Upgraded RAM gives instant performance boosts across your system, without voiding your warranty.

Crucial has a good name among resellers and we had no problems with the RAM in an iMac. We could offer some benchmarks about this stick but chances are you would just fall off your chair with boredom. Suffice to say it will save you cash to buy direct and it's certainly a sensible investment if you've only got 512MB at the moment. James Ellerbeck