The Windows 8 Developer Preview was downloaded 500,000 times in the first 12 hours it was available, Microsoft has revealed.

The pre-beta build was posted to the Microsoft website shortly after 1am GMT on Wednesday, just after the tech giant officially unveiled the next iteration of the Windows operating system.

See also: Microsoft Windows 8 review

The downloads, which range from 2.8GB to 4.8GB in size, come with no restrictions and mark a different approach compared to that taken with Windows 7. When Microsoft debuted a similar developer preview of Windows 7 in October 2008, it didn't allow the general public to download it. However, within hours, the Windows 7 preview was leaked to online file-sharing sites.

The 4.8GB download is a 64bit edition of the Windows 8 Developer Preview that also includes developer tools such as a preview of Microsoft Visual Studio 11 Express and the SDK (software developers kit) for Metro-style applications. Metro is Microsoft's name for the Windows 8 tile-based interface that borrows heavily from Windows Phone 7.

Two other editions, a 64bit (3.6GB) and a 32bit version (2.8GB) of the operating system, can also be downloaded.

"You could say that if Windows 8 is Windows reimagined, we're also in the process - and Windows 8's an important step of that - of reimagining Microsoft," said CEO Steve Ballmer.

"While it's clear we have a long way to go still with Windows 8, we've been gratified certainly by the reactions and the interest."

All downloads are available as a disk image in .iso format that must be copied on to a DVD or USB flash drive for installation purposes. The software requires a PC with 1GB of RAM (2GB for the 64bit edition) and 16GB of hard-disk space (20GB for 64bit).

It's worth noting that to install Windows 8 and the developers tools, users must overwrite the machine's current operating system (XP, Vista or Windows 7) with a clean install. The smaller sans-tools versions, however, can be installed while retaining the files, user accounts and settings on a Vista- or Windows 7-powered PC

The Windows 8 Developer Preview can be downloaded now from the PC Advisor downloads site.