Windows 8 team blog:
Windows Update and handling restarts on Windows 8
….we made the following improvements to the Windows 8 updating experience.
WU will consolidate all the restarts in a month, synchronizing with the monthly security release. This means that your PC will only restart when security updates are installed and require a restart. With this improvement, it does not matter when updates that require restarts are released in a month, since these restarts will wait till the security release. Since security updates are released in a single batch on the second Tuesday of every month, you are then getting essentially one restart a month. This simplification helps in three ways: it keeps the system secure in a timely manner, reduces restarts, and makes restarts more predictable.
There is one exception to the rule to wait for the monthly security release, and that is in the case of critical security update to fix a worm-like vulnerability (for example, a Blaster worm). In that case, WU will not wait, but will go ahead and download, install, and restart automatically. But this will happen only when the security threat is dire enough.
WU notifies you of any upcoming automatic restart. Let’s assume that WU has already detected, downloaded, and installed security updates, and now requires a restart. Windows Update will notify you of an upcoming automatic restart through a message on the login screen that will persist for 3 days. Because the majority of update activity occurs in the first three days of the release of each update [see Figure1], we wanted to give you 3 days to allow you to restart at your own convenience. You would restart by selecting “Update and shutdown” or “Update and restart” on the login screen, or by going to Windows Update in the Control Panel. You will no longer see any pop-up notifications or dialogs about pending restarts. Instead, the message appears in a more visible and appropriate place (the log-in screen). The use of the login screen has become ubiquitous even in home environments, as more and more machines become portable.
Here is a timeline view of that experience:
1. A message about the upcoming restart is shown in the login screen for three days or until the PC is restarted (whichever is sooner). This means you now have three days to restart the PC at your convenience. All you need to do is see the login screen once in 3 days to see the message about the upcoming restart and by default the lock screen will appear after 15-minute idle timeout.
2. In addition to the restart notification on the login screen, the Power options on the lock screen will change to “Update and restart” immediately after the update occurs, and will include “Update and shutdown” on days two and three, to make the message even more apparent to you. This allows you to restart your PC at your own convenience.
3. If after three days, the restart still has not occurred, then WU will automatically restart your PC for you. In this case, the automatic restart will happen either at the end of the three-day grace period, or, to prevent data loss if WU detects that there are critical applications open at the end of the three-day grace period, it will wait to automatically restart the next time you login. I’ll address this behavior in more depth in the next section.
4. After the restart has occurred, the message on the login screen will go away and the power options will revert to the original choices. We know people would like Windows to automatically log in after the restart, but we strongly advise against doing so, given the potential security issues with this configuration.
Delay the automatic restart if there is potential of losing user data. If the PC has hit the three-day deadline and still needs an automatic restart, WU will only automatically restart the machine if there is no chance of losing the user’s data. That means, if you are not at your PC (i.e. it is locked), if you have applications running in the background, or if there is potentially unsaved work, WU delays the automatic restart until the next time you come back to your machine and log in. At log-in, you will be asked to save your work, and you’ll see a warning that the machine will be restarted within 15 minutes.
Ensure minimal interruption to user activity. Having a restart notification or dialog pop up in the middle of an important presentation, a game or a movie is not a pleasant situation, to say the least. When attempting to automatically restart the PC, if you are in presentation mode, playing a game, or watching a movie full-screen, WU detects this state, and delays the automatic restart until the next available opportune moment or the next time you log back in to the PC.
The experience for business users. For PCs in an enterprise setting, if no policy has been set by the IT administrator, the updating experience is exactly the same as it is for home users. However, an IT administrator can set a policy to prevent auto-restart after automatic installs (just as in Windows 7). If they set this policy, there will be no three-day countdown and no automatic restart. Instead, users will see a message on the login screen indicating that the PC needs to be restarted, and the message persists until the restart occurs. This informs users that a restart is required while keeping them in control of when to restart.
The experience for users in “notify mode.” I also want to address the experience for users who have chosen to be notified before downloading or installing updates (5.82% of the WU user base from Figure2). For a user in this “notify mode,” a message will be shown on the login screen. If you choose to be notified before downloading updates, you will see the login screen message saying “Important updates are ready to be installed” when updates are ready to be downloaded. If you choose to be notified before install, you will see the same login screen message after updates are downloaded, but before they are installed. In either case, you won’t see the message about a pending restart on the login screen since installation is not automatic.
Cumulatively, these improvements help us achieve the balance we are striving for with Windows Update - keeping the PC (and PC ecosystem) up-to-date, without an intrusive experience.
Full Story: Minimizing restarts after automatic updating in Windows Update - Building Windows 8 - Site H