Use Microsoft’s new Windows 7 operating systems for 30 days without formally activating it with a paid-for product key.

No, wait … we meant 120 days.

After various reports were published on the Web, including one by Computerworld, Microsoft has confirmed that PC users can initiate a reset command up to three times, thus adding 90 further days to the stock 30-day grace period for activating the product with Microsoft.

The extension is accomplished by calling up the “rearm” switch that will reset the countdown timer back to 30 days. Here’s how it’s done:

1. Start the command line by clicking Start > All Programs > Accessories > Command Prompt (Run As Administrator) –- or for a shortcut, hit the Windows Key + R and type “cmd”.
2. At the command line, enter in “slmgr –rearm” without the quotations.
3. Restart Windows 7.

A similar procedure was available for Windows Vista. Microsoft says extending the grace period does not violate the Windows 7 End User License Agreement (EULA). There are more details on the extension process, and some caveats, at Windows Secrets.

Product activation has been around for some years, showing up in Windows XP and, later, Vista. Since 2008, if the computer was not legally activated with a key code, it would descend into a “reduced functionality” mode after 30 days, with the OS dropping into a black background and flashing persistent reminders to the user to activate.

Retail versions of the new OS go on sale in October.