Anyway this discussion is about a new capability added in Windows 10 version 1607 Anniversary Update. I stumbled on this when checking for new updates.
Go to Windows key + Check for updates
In the left-hand column, click on "Windows Defender."
Scroll down until you see "Windows Defender Offline". Click on "Scan Offline".
After you click this button, your computer will automatically reboot and begin scanning your PC for malware. The scan may take up to fifteen minutes. If any malware is found, you’ll be prompted to clean it up from within the Windows Defender Offline interface. If no malware is found, your computer will automatically boot back into Windows once the scan is complete.
For me it ran a "Quick scan" and took just under 4 minutes.