Windows 8 is rolling out in stunning fashion, attracting millions to install the newest version of the Microsoft operating system barely a week after its launch, company chief executive Steve Ballmer said on Wednesday.

Informing attendees of the Microsoft-sponsored BUILD Conference for developers in Redmond, Washington, Mr Ballmer said tens of millions enterprise customers have migrated to the revamped Windows environment, which was redesigned to allow for computing smooth computing experience on traditional PCs, smartphones and tablet computers.

"The level of embrace from enthusiasts is very, very high ... In just the last three days, we have sold four million Windows 8 upgrades," the Microsoft CEO was reported by Agence France Presse (AFP) as saying.

The figures shared by Mr Ballmer were understood to mostly consist of conventional computing tools as the mobile version of Windows 8, the Windows Phone 8, will only start hitting international markets this weekend, capping the biggest marketing push undertaken by the software giant since the first version of its core product was introduced decades ago.

The cross-platform Windows 8 also represents the company's attempt to play a bigger role in the multi-billion dollar mobile device industry that is now dominated by Apple and Google, analysts said.

Microsoft's Windows RT-powered tablets and WP8 smartphones will soon be pitted against Apple and Android mobile gadgets that already sold hundreds of million units since they first captured consumers' imagination five years ago.

For Windows 8 to woo users in big numbers, Microsoft needs to quickly beef up its collection of mobile apps, which the tech giant said now number at around 120,000 and counting.

Apple may have been credited with re-inventing the modern mobile phone but Microsoft is adamant that its cohesive approach in selling the latest Windows OS and products revolving around it, said Joe Belfiore, the tech firm's corporate vice president.

The Microsoft focus is to convince buyers that the new integrated Windows setting, mobile and traditional, "puts people at the centre of the experience," Mr Belfiore told AFP.

Windows 8 is essentially transforming Microsoft from a software-centric company to a full-service firm that is not only able to provide attractive computing devices but also the whole productivity and entertainment experience, Mr Ballmer had earlier said.

For instance, everything about Microsoft can be had by buying the Surface tablet or tablets manufactured by partner vendors and WP8 smartphones, which were designed to readily access the company's full range of online and social media services, the company chief added.