Why is updating Windows 10 slower than installing it?

Question

Recently, I had to install a new Windows 10 system. Installation from a USB key took probably about 15 minutes (I didn't watch the clock accurately to determine the exact time to a minute precision). However, when Windows noticed there are updates for Windows 10, the update process (not downloading the updates but installing them) takes essentially forever. An hour and the system isn't still updated. Not sure how many hours it takes to update it.

Is there any technical reason why installation of updates is slower than installing the whole system? As far as I understand it, the update process should touch only a (large) subset of the files on the hard disk, whereas the installation process should touch every single file on the hard disk. So, according to my logic, updating the system should be faster than installing it from a USB key. Note the update time I mentioned doesn't include download time (which was relatively fast), so poor Internet connection speed can't be the culprit.

Answer 1

Installing the system is done on what is effectively an empty disk. Installing is effectively a dumb copy process followed by a setup and configuration of drivers.

The disk does not have any programs or operating system services or virtual memory (page-file) requirements that are competing for access to it. The operating system is, at the point of installation, running entirely from the boot media and memory only.

Even if the configuration step is demanding in terms of disk access, the system is not competing with itself and other programs to do it.

Once installed the system is running from the same disk that is being updated, the system has a page-file that is being used to service virtual memory demands, other programs are using the disk, services are doing their own work as well.

Updates also require a lot more steps:

• download patch file
• extract patches
• create a system restore point
• check the version of existing file
• move/delete existing file
• copy new file
• make system configuration changes

And possibly more.

Working on a live system is a lot harder than working on an "offline" system. If there were a way to take the system offline to perform the updates then it could be a lot faster, but this is mostly unacceptable to almost all users. We still have this with the major point-releases, but we don't want it to happen on a regular basis.