Microsoft has started the roll-out of its new operating system, Windows Vista, which at first is being made available to business customers only.
HQ: Redmond, Washington
Operating profit: $16.5bn
Windows sales: $13.2bn
Office sales: ~$10bn
Financial year to 30 June 2006
Source: annual report 2006
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.
A huge but slow success
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.
Microsoft predicts that Vista will be the fastest-selling operating system to date.
Start: Vista users will not have to learn Windows from scratch
Experts agree, but say this is merely a result of the wider usage of computers compared to five years ago, when Windows XP launched.
Corporate customers, meanwhile, will take their time deploying Vista as well.
"Our big corporate customers were the first to test Vista, but will probably be the last to introduce it, because they have the most [hardware and software] to test for compatibility with Vista," said Gareth Hansford, managing director of Lenovo UK, the company that was IBM's PC division until it was bought by Lenovo of China.
He expects corporate customers to begin large-scale rollouts of Vista in about a year's time.
IDC's Al Gillen agrees, and points to a very unusual feature built into Vista, which allows IT managers to "downgrade" the software on new computers and run Windows XP instead.
Once the company is fully Vista-ready, the IT team can simply activate the original Vista license bought with the new PC.
Most analysts believe that Vista will dominate computer desktops in about two years' time.
Microsoft's core product
Vista Home Basic
Vista Home Premium
Microsoft has combined the launch of Vista with the release of the newest version of its productivity software, Office 2007, and its networking software Exchange.
The company has invested a lot of money and effort to get Vista ready.
More than 10,000 workers reportedly have worked on getting the operating system ready for deployment.
The development of Office and Vista took five years and $20bn (£10bn), said Gordon Frazer, managing director of Microsoft UK, at the product launch in London.
Microsoft executives say that Vista is designed to be much more secure than any of its previous operating systems, while home users can look forward to much better game play and the integration of Microsoft's media centre into the main operating system.
A key feature of Vista and Office 2007 is the integration of desktop search, which will make it much easier for users to find both applications and files. According to Microsoft, less than 6% of computer users currently have products like MSN and Google desktop search installed on their computers.
The XP successor will come in six versions, from very simple installations for low-powered computers to fully-loaded corporate editions.
Vista's success is crucial to Microsoft's finances.
The corporate division responsible for Windows is generating nearly a third of Microsoft's turnover, and a much higher share of its profits.
The suite of programs - encompassing a word processor, spreadsheet, database and more - can run on both Windows XP and Vista.
Microsoft says that the combination of Vista, Office 2007 and Exchange combined will allow corporate customers to make hefty productivity gains.
Jacob Jaffe, director of the Microsoft Office programme, told BBC News that surveys of test users of Office 2007 showed that nearly four-fifths of them reported productivity gains as a result of using the software suite.
Several rivals of the company, however, have complained that Vista's new design is making it more difficult for them to get their products to work - for example anti-virus software.
The dispute is likely to put Microsoft under scrutiny again, with the European Commission already voicing concerns whether Vista is shutting out competitors.