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Why does Windows apply updates when shutting down AND turning on? I'm working on Windows 7 and would like to know if this can be disabled. It's really bad when I need to leave and turn off my laptop to have it go through a bunch of updates. It's also annoying when I want to use a computer and don't expect to wait for updates to be installed. If Microsoft wanted to force people to install updates why can't Windows wait until the user has logged in and started working?

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@kinokijuf I know what it is doing, it is completing the update I asked it to do because it could not perform the update on a live/shutting down system. Also if you want to know EXACTLY what a individual update is doing you can go to the MSDN Knowlage Base Article for a specific update and see what it is replacing (for example the recent true type patch KB2779030, see the "Windows 7 and Windows Server 2008 R2 file information" section). – Scott Chamberlain Jan 3 '13 at 17:53
This should help reduce the nagging in Win7. Minimizing restarts after automatic updating in Windows Update details the improvements made in Win8. – Karan Jan 3 '13 at 18:33
You don't have to install available updates when shutting down. There's an option on the shutdown menu which reads something like "shutdown without updating". – Harry Johnston Jan 4 '13 at 2:19
In my case it just decided to install 13 pre-shutdown updates on a Windows XP computer that was already up to date--I thought. I sure hope I'm not getting pwned. Anyone else seeing this? – user187151 Jan 11 '13 at 8:39
up vote 9 down vote accepted

Some updates require that system dlls are replaced.

The way that Windows works means that these often can't be replaced while a user is logged in so the machine has to be rebooted to allow this.

You can get the update to happen while you are still using the machine, but once it's complete it will nag you to reboot. You can postpone this, but you will eventually have to do it.

As to why Windows 7 performs part of the update on shut-down and the rest on the next reboot I'm not sure - unless it's because certain files are still in use at that point or as Robert points out the update needs to access the registry which needs to be done early in the boot process to prevent hijacking.

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Some updates require registry patches, which are done very early on in the boot process to prevent hijacking. – Robert Harvey Jan 3 '13 at 17:41
@RobertHarvey - ah. Makes sense. – ChrisF Jan 3 '13 at 17:42
This is all correct. In addition, you should mention that it's possible to replace most of the ancillary files on a system by rebooting all of the available services, so that replaces in memory everything but the very most core of Windows in-use files. However, that requires the following: user-permissions to reboot services, you would have to disclose what was being replaced and why (this can be determined by a careful hacker, but do you really want that minutiae?), a more thorough process to ensure everything is properly re-initialized and/or shut-down. Ergo, easier to just reboot. – jcolebrand Jan 3 '13 at 17:57
Because of the way Microsoft has determined that it's easier to just let people reboot, they have built the nagger services to remind you to reboot. If they did the above, there would be no need for the naggers. Just know that they have spent a LOT of money and time on research to make the system "easier for you to operate" at the expense of a few things, such as consistency requirements, and sanity checks, since they can't oversee all 500 million + computers in the wild. And remember a great many updates don't require a reboot. I do those all the time. IT's the core that reboots you. – jcolebrand Jan 3 '13 at 18:02
Note also that Linux filesystems often allow you to overwrite an in-memory-use file by shadowwriting the file (it keeps two copies until the one is finished being used) whereas Windows wants to help you, so doesn't allow that. Otherwise you could get by with a lot less reboots. – jcolebrand Jan 3 '13 at 18:03

Windows does that when the files it needs to update are in use during the normal operation of the operating system.

It attempts to get as many as it can while shutting down but there are still some core files that must be used to perform that update, what it does in that case is catch those files next time the OS boots before the files get used for the first time.

Also some updates require registry patches, which are done very early on in the boot process to prevent hijacking. (Thanks Robert)

This cannot be deferred "until the user logs in" because the files would be in use again so therefore could not be replaced.

The only thing you can do is run the update manually by hand (updates come out the 2nd Tuesday of every month unless it is an emergency patch) when you are not in a rush.

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