It is not just an "update" patch Baz. It is a complete operating system to replace the original. It also happened with w7 wxp and w8 so is not unusual. To effect this upgrade Microosoft has to check your system for capacity and security, then install the new system after finding disc space if your system is near to capacity. After that it has to transfer all your files and settings over to the new system and check that all is correct and good to go. Then the old operating system is removed and your system is restored after a reboot. It will take longer for some due to slower systems and differing broadband speeds around the Country. I did a desktop in just under 1&1/2 hours whilst on line and with other devices connected to the router but did a laptop in an hour by disconnecting all other devices from the router including phone, printer, tv, and my music centre.