All are available as a disk image in .iso format that must be copied onto a DVD or USB flash drive for installation purposes.

The preview requires a PC with 1GB of RAM (2GB for the 64-bit edition) and 16GB of hard drive space (20GB for 64-bit).

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.

As it typically does when it releases early-look software, Microsoft warned casual users to steer clear of Windows 8.

"The software is provided as is, and you bear the risk of using it," said Microsoft on the download website. "It may not be stable, operate correctly or work the way the final version of the software will. It should not be used in a production environment."