Microsoft has made a preview of Windows 8 available to download.
Windows 8 Developer Preview, as Microsoft called the pre-beta build, was posted to a company website late on Tuesday.
The downloads, which range from 2.8GB to 4.8GB in size, come with no restrictions, a company spokeswoman confirmed earlier in the day.
Microsoft gave customers their most-detailed look yet at the new operating system during a two-and-a-half-hour presentation at its BUILD Windows conference, which opened Tuesday and runs through Friday.
When Microsoft debuted a similar developers preview of Windows 7 in October 2008, the company limited the early look to attendees at its Professional Developers Conference (PDC), and told the general public to wait for a beta early the next year.
Within hours, the Windows 7 preview leaked to online file-sharing sites.
Microsoft has made such leaks moot by offering Windows 8 itself.
On a new Windows Dev Center site, Microsoft provided links to three different versions of Windows 8.
The largest weighs in at 4.8GB and is a 64-bit edition 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 64-bit version (3.6GB) and a 32-bit version (2.8GB) of the operating system, can also be downloaded.
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."
Attendees of BUILD were given the preview on a special-edition Samsung slate-style PC .
The Windows 8 preview can be downloaded from Microsoft's site.