Microsoft has announced the global availability of its Windows 8 operating system, Digital Spy said.

The new software, compatible with more than 1,000 certified PC and tablet models, marks the platform's most significant overhaul since Windows 95.

Windows 8's features include a brand new user interface, a wide range of applications and a dedicated storefront called the Windows Store.

"We have reimagined Windows and the result is a stunning lineup of new PCs," said Microsoft CEO Steve Ballmer. "Windows 8 brings together the best of the PC and the tablet.

"It works perfect for work and play and it is alive with your world. Every one of our customers will find a PC that they will absolutely love."

The new OS will be available to download to upgrade existing PCs in more than 140 markets and 37 languages from 12.01am on October 26.

Windows 8 comes in two primary versions, Windows 8 and Windows 8 Pro, as well as Windows 8 Enterprise for large organisations. The new Windows RT version will be available for ARM-based tablets.

Users running Windows XP, Windows Vista or Windows 7 can upgrade their machines to Windows 8 Pro for around $39.99 until the end of January.

Customers who purchased a Windows 7 PC between June 2 this year and January 31, 2013 can upgrade for around $14.99 as part of Microsoft's Windows Upgrade Offer.

Microsoft has also launched its Surface slate in various territories, marking its entry into the tablet hardware market.