Hard drives are about to undergo one of the biggest format shifts in 30 years.

By early 2011 all hard drives will use an "advanced format" that changes how they go about saving the data people store on them.

The move to the advanced format will make it easier for hard drive makers to produce bigger drives that use less power and are more reliable.

However, it might mean problems for Windows XP users who swap an old drive for one using the changed format.