Apple will launch the client and server upgrades to its Mac OS X version 10.4, codenamed Tiger, at simultaneous worldwide events at 6pm BST tonight.

"Our competitors will be trying to copy Tiger's features and innovations for years to come," said Philip Schiller, senior vice president of worldwide product marketing at Apple.

New features include a search engine called Spotlight that can go through the entire contents of the computer quickly to find files. It is similar to, but more feature-rich than, Google's desktop search tool.

Another new application, called Dashboard, lets users build a page of 'widgets', small updatable functions like a clock, weather forecast or travel information. The system is similar to services like Konfabulator.

Other new features include an enhanced iChat service with videoconferencing and the ability to link 10 callers simultaneously.

Six-hour launch events including technical seminars will be held at UK Apple stores in Birmingham and London. A PowerBook G4 and an iPod will be given away, and staff will be on hand to help users upgrade their systems.

The client version of Tiger will cost £89.99 compared to $129 in the US, a price mark-up of around 25 per cent.

There are versions of the server software available for 10 and unlimited clients costing £349 and £699 respectively.