Windows 8, the next major upgrade of Microsoft's operating system for PCs, tablets and laptops, will be released to manufacturers in August and will ship commercially in October, the company has announced.

Microsoft had previously said that the OS would be commercially available before the end of the year but hadn't given a firm shipping date.

When Windows 8 is released to manufacturers (RTM), Microsoft will also activate the Windows Store and start charging for applications, which during the test period have been free, the company announced at its Worldwide Partner Conference in Toronto.

In a keynote appearance at the conference, Microsoft CEO Steve Ballmer said that this is "an epic year" for Microsoft because of all the new product upgrades it's delivering, in particular Windows 8, which he called "the biggest deal for our company in at least 17 years."

The timetable Microsoft announced today applies not only to the Windows 8 version for x86 chips from AMD and Intel, but also for Windows RT, the Windows 8 version that will run on ARM-based devices. Windows RT will ship embedded with its devices, which will be made by Microsoft and third-party hardware partners. It will not be sold as a stand-alone OS like Windows 8 for x86.

At the time of commercial availability, Windows 8 will also be available for upgrades for people with PCs running Windows 7, Windows Vista and Windows XP. Microsoft has already provided details about upgrade options and prices.

Windows 8 will be available in 109 languages and 231 markets worldwide.

To date, Microsoft has sold more than 630 million licenses of Windows 7, and more than half of enterprise desktops today are running it.