The company published the latest release candidate build of the new Windows for widespread user download on Tuesday.
Microsoft is warning users against rushing to download the update, as the software will be offered until the end of July without a download limit.
Downloads will remain valid until 1 March 2010, when the operating system will begin shutting itself off every two hours in the run-up to the 1 June expiry date.
Microsoft is also encouraging users to back up their data before installing the update, particularly those running Windows XP or the Windows 7 beta, which require a "clean install" of the update.
The release candidate is set to be the final version of Windows 7 before the company unveils the retail version. Microsoft has officially set a loose target date of early 2010, although some vendors have claimed that the software could be out as early as October of this year.
Among the new features in the release candidate are new security protections, and a virtualised XP Mode for legacy software.