By design, Windows 7 offers a command which extends your grace period period up to 120 days. During this period you’re able to receive Windows updates and security patches. So, basically, you can use Windows 7 without providing a key for 120 days.
This action can be done on any version of Windows 7 and it’s completely legal.
So, how can we do it and what is the best way to do it?
Once you install a fresh copy of Windows 7, you can use the Computer Properties to view the remaining grace period.
Hit Windows ORB and type ‘System’ select the ‘System’ link from the start menu under ‘Control Panel’ section.
Scroll down and under ‘Windows Activation’ part you will see the remaining grace period.
Use the Windows normally until the grace period ends, then open the command prompt and type the following command:
slmgr -rearm
After a moment you will see a confirmation message saying that command has completed successfully. Reboot afterwards.
When you check the System Properties again, you will see that the grace period has been extended to 30 days (again).
This command can only be run 3 times! So, to use the maximum grace period of 120 days, you should use it only when your current 30-day grace period window has expired.