Microsoft Windows 8 is going to be launch or relasing in the first week of August, and will move to general availability for everyone by the end of October, Microsoft has announced.

The most updated operating system featuring ‘Metro’ interface likely to be available as a download.

Speaking at Microsoft’s Worldwide Partner Conference in the US, Tami Reller, the vice-president for Windows, gave the dates when the finished software would be sent out to companies so that they can test and include it on PCs – the “release to manufacture”, or “RTM” date – and the later date when people will be able to buy and download it directly from Microsoft.

Microsoft has already announced a scheme which mean that people who bought a PC running Windows 7 after 2 June will be able to upgrade to Windows 8 for just $15.

Windows 8 will automatically be included as the basic system on PCs that go on sale from late October, or possibly before. Microsoft will also offer a free cloud storage account using its SkyDrive system to every Windows 8 buyer.

Microsoft is introducing a new system for buying third-party software, called “The Windows Store”, with Windows 8. That will only offer approved and checked software for sale.

Windows 7 was available in both boxed and download forms, and Windows 8 is expected to follow the same pattern.

Windows is a key revenue and profit generator for Microsoft, with about 400m PCs being sold every year around the world, each generating an average about $50 of revenue and $35 of profit per machine; profits from the Windows division makes up more than half of Microsoft’s quarterly profits.

But recently is has come under assault from the rise in smartphones and sales of tablets, particularly Apple’s iPad, while sales of PCs have been showing slowing growth and even reverses. That has led Microsoft to re-magine the interface for Windows, with the “Metro” interface of Windows 8 offering the most radical departure in experience since the introduction of the Start button in Windows 95.