Microsoft has started the roll-out of its new operating system, Windows Vista, which at first is being made available to business customers only.
The system, a replacement for the firm's current Windows XP operating system, will not be available to home consumers until the end of January.
With Windows running on nine in 10 of the world's PCs, analysts agree the new version should be a big success.
However, Vista is two years late and its consumer launch misses Christmas.
Last minute delays at Microsoft meant that computer makers would have been able to install Vista only on about half the computers that they were hoping to sell over Christmas, said Al Gillen, a Vista expert with technology consultancy IDC.