REDMOND, Washington: Microsoft is nearly done with a much-anticipated overhaul of its Windows operating system.    

The software maker signaled the makeover is nearly complete with Thursday's release of the final test version of Windows 8.

Windows 8 is considered to be the biggest change in decades to Microsoft's widely used operating system. The software displays applications in a mosaic of tiles and has been designed so it can run desktop, laptop and tablet computers.

PC sales have slowed in the US as consumers delay replacements and instead buy mobile devices such as smartphones and tablet computers. The versatility of Windows 8 is expected to spawn a new generation of computers that are part laptop, part tablet.

The latest test version of Windows 8 is available in 14 languages and includes several improvements from a less-refined version released three months ago. The upgrades include more ways to connect to other Microsoft services, more security controls and more touch-screen features.

Microsoft Corp. hasn't announced when Windows 8 will go on sale yet. Most industry analysts expect the software will be available in September or October.

With Windows 8 looming, more prospective computer buyers may delay their purchases until the new operating system is available.

Microsoft is trying to discourage procrastination with a special promotion that begins Saturday in the US, Canada and more than 120 other markets.

The program allows buyers of computer running on Windows 7 to upgrade to Windows 8 Pro, when it's available, for $14.99. Microsoft hasn't announced other prices.