An unsupported version of Windows will no longer receive software updates from Windows Update. These updates include security updates that can help protect your PC from harmful viruses, spyware, and other malicious software which can steal your personal information. Windows Update also installs the latest software updates to improve the reliability of Windows—such as new drivers for your hardware.
When does support end for my version of Windows?
Check the end-of-support dates for your version of Windows.
If your version of Windows is still supported, you should always be sure to install the latest updates or service packs for Windows. You can download and install these through Windows Update.
Will I still be able to use Windows after support ends?
Yes, even if you have an unsupported version of Windows XP or Windows Vista, Windows will continue to start and run. You just won't be able to receive software updates from Windows Update any longer.
For full details about the support policy, see the Microsoft Support Lifecycle Policy FAQ.