Apple plans to launch the next version of its OS X 10.5 operating system, code-named Leopard, in the spring of 2007.

Developers attending the company's World Wide Developers Conference in San Francisco this week will receive a first preview version.

Apple does not release public betas and developers have to sign a non-disclosure agreement to prevent new details about the software leaking out. However, at the event the company provided a brief preview of several of the application's new features and technologies.

The operating system will introduce a new backup and recovery technology, dubbed Time Machine, that promises to make constant back-ups of the hard drive.

"If your hard drive dies, you buy a new hard drive, you put it in your machine and you will be right where you were when that hard drive died," Scott Forestall, Apple’s vice president of Platform Experience told delegates.

The technology uses a secondary hard drive such as an external backup device.

Time Machine will also let users recover items they have deleted or restore files to a previous version if a document is accidentally overwritten.

Another new technology introduces virtual desktops to the operating system. Referred to as Spaces, it allows users to organise their applications in one of four desktops to prevent them from cluttering their desktops.

In a demonstration Apple chief executive Steve Jobs showed one Space running Mail and the Safari browser, while a second would hold a sound recorder and website publishing software to create a podcast.

"Spaces is a new way of working on your Mac," said Jobs.