Retailers say the first copies of Microsoft's latest operating system have proved a hit with shoppers.
The Windows XP went on sale at midnight in some UK stores, with pre-orders double the expected level.
A handful of shoppers queued outside HMV in London's Oxford Street to buy the software.
The store was also the venue for a world record attempt by pop group the Electric Soft Parade to make the fastest ever music video in under four hours using the system.
Simon Bear, 24, from north London, who works in advertising, came to try out the system and says he was impressed.
He adds: "I'll come back to buy it at the weekend after I've been paid."
Windows XP can be installed on computers under two years old updating existing Windows technology to offer improved reliability and built-in multimedia functions.
The launch of Windows 95 six years ago saw computer sales rise and the industry hopes Windows XP can help reverse the 11.3% slump in world computer sales since the US terror attacks.
The software was officially launched in the Royal Festival Hall in central London by Microsoft chief executive Steve Ballmer.
The company says orders for Windows XP had topped the Amazon charts and pre-orders were double those anticipated, running into many thousands .