Microsoft has launched the most complete preview yet of its forthcoming Windows 8 operating system.
The company said that tens of thousands of improvements have been made to what it calls the most important redesign of its interface since Windows 95.
Consumers can now download the release preview of Windows 8, a system which Microsoft says is its most tested operating system ever.
It is expected to go on sale in the autumn, three years after Windows 7.
The new operating system is designed to bring Windows into the touchscreen, smartphone era.
It adopts the Metro interface of the company's mobile operating system, Windows Phone 7.
Windows, which still dominates the desktop PC software market, has been much slower to make an impact on mobile phones and tablet computers.
The release preview has features not available in the last version, the consumer preview, launched in February.
There will be new apps for the Bing search engine, news and sports, and improvements to the mail and photo applications unveiled previously.