The next version of Windows, dubbed Windows 7, is allegedly well past the drawing board. Early alphas are already circulating with key Microsoft partners, and the final version could be with us by the end of 2009.

But do we really need a new version of Windows, when lots of people haven't even upgraded to Windows Vista yet? And even if you have upgraded to Windows Vista, will you be ready to move on again in just a couple of years' time? The upgrade path isn't exactly cheap.

Almost no features of the new version of Windows 7 have been publicly revealed just yet. But the problem isn't the features, or whether these are worthwhile.

Although you can levy criticisms at Windows Vista for numerous bugs, such as the many game incompatibilities, you'd have to be a pretty firm Microsoft hater not to agree that Vista is packed with impressive technology.

There's the fully integrated search, and handy desktop gadgets. The new driver model, with greater emphasis on user mode, means your graphics card is far less likely to take down your whole operating system. Windows Vista is very pretty, too. The 3D graphics-powered Aero interface certainly makes XP look rather 20th Century. And the bundled applets are much improved, such as Windows Mail.

Despite all this, Windows Vista just doesn't feel as essential as Windows XP. In fact, if you were a Windows NT and 2000 user, even XP wasn't exactly a sea change - just evolutionary eye candy on top of the same basic NT core. But for most of the computing world, swapping from Windows 9x or Millennium, with its DOS heritage, to XP was a huge leap.

The biggest difference was the change from co-operative to pre-emptive multi-tasking. Instead of applications having to 'play fair' and give each other a slice of processor time, the operating system takes more control. This is a major reason why Windows NT, 2000 and XP don't freeze up as much as the Windows 9x OSes used to.

So although the overall memory requirements are greater for XP than Windows 9x, XP generally felt like a step forward for most consumers.