Microsoft Corporation's forthcoming update to its personal computer operating system will be called Windows 8.1 and will be available later this year free to existing Windows 8 customers, the marketing chief for the Windows unit said on Tuesday.

The world's largest software company has been touting the update, previously code-named 'Blue,' as a series of improvements to the Windows 8 software, launched in October, which has not been as popular as it had hoped.

Microsoft has sold 100 million Windows 8 licenses in the six months since launch, roughly in line with the previous version, but wants to combat sputtering interest in its flagship software with a substantial update to make it easier to use and compatible with smaller tablets.

"Windows 8.1 will be delivered as a free update to Windows 8 and to Windows RT and it will be easy to get right from the Windows start screen through the app store," said Tami Reller, head of finance and marketing at Microsoft's Windows unit.

A preview version of Windows 8.1 will be made available at the start of Microsoft's annual developer conference on June 26, Reller said, with the finished update released later this year. – Reuters