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."

Windows 8 will hit its RTM milestone in early August and will begin shipping commercially in late October, according to Microsoft. Those dates apply 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.