Buyer's Guide Despite advances in other kinds of storage, hard drives are the backbone of the vast majority of desktops and notebooks.

And they are still the most cost-effective way of adding extra storage capacity to an older machine. They are cheap to buy, easy to use and remarkably robust in service.

Typical warranties run from three to five years and, if that’s running continuously, as it could easily be for a drive in a server, that equates to more than 40,000 hours of use.

Compare that service life with that of a typical projector lamp, at around 2,000 hours, or of an electric drill, rumoured to be less than 20 hours.

While the prices of hard drives continue to fall, their capacity goes on climbing, so the overall cost per gigabyte is getting lower and lower.

A 2TB drive, for example, can be had for about £70, a cost of 3.5p per gigabyte. Compare that with a rewritable DVD at around 9p per gigabyte, or a Blu-ray disc at about 29p. Memory sticks and cards can only manage 38p or so, at best.

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Drive types

There are two drive form-factors in common use: 3.5in, normally reserved for desktops and servers, and 2.5in for notebooks. You can also buy 1.8in drives, which are mostly for specialist applications such as some media players.

Most hard drives now use Sata to connect to the host computer, although IDE devices are available, mainly for older machines.

The advantage of Sata devices is a simple data connection: a small, seven-core cable rather than a 40-wire ribbon.

Notebook IDE drives use a 44-wire ribbon, with the extra connectors providing 5V power. Before buying an internal drive, don’t forget to determine which type of interface is used by the device you are buying the drive for.

External hard drives may be 3.5in or 2.5in, but they are housed in robust cases and generally connect by USB, or less commonly Firewire or eSata (external Sata). They can be Sata or IDE inside the case, but this will be transparent in use.

The 3.5in external drives need separate power, either from a supply inside the drive case or from a separate block, normally supplied with the drive.

External 2.5-in drives can often draw all the power they need from the same USB connection they use for data, and are therefore more convenient. That, plus their smaller size, has made them the standard for portable drives.

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