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The question is similar to this one except it's for drivers.

Why do I need to restart the computer after installing new drivers? For example, if I did a fresh install of Windows 7, installed audio drivers on it, the sound works fine without restarting yet the installer still asks for a restart.

I'm assuming it's a similar reasoning as "because users are stupid", but I'd like to hear a technical reason for this.

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I would like to share this link with you to an answer from 2010 on this website - I never make a point of restarting after a driver update if I am actively using my machine, only after a system update (for security reasons) and all works out just fine. – denis12345 Feb 7 '13 at 8:04

The simplest technical reason is because "they're in use".

If you create a picture file in paint, save it, but don't close paint and try to delete the file. Explorer will say it can't because its in use.

This is basis for the restart, its only when booting that Windows can guarantee not one program was using the drivers files.

In later versions of Windows they built well defined wrapper layers (or boundaries) around certain areas (like display). The layer talks to the underlying driver, but it also is the only program that could ever use that driver, so its a simpler case to 'disconnect' the driver and replace it.

I think in Linux and OSX this layered approach is more fundamental in the design and so they rarely if ever need reboots.

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Nowadays, this has mostly historical reasons. As you have noticed, most Windows drivers today can be installed "on the fly", that means they work without reboot. However, that hasn't always been the case, previous versions of Windows and previous hardware generations needed more complex setup procedures that could only be done at boot. Today, manufacturers are either lazy and don't adapt their installers or ignorant of the possibility of not needing a reboot or they just want to play safe. And with Windows, still, it's always a safe bet to just reboot to iron out possible quirks.

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In many cases you are still using your 'old' drivers until your system is rebooted. Even though the properties of the device may display the new driver version in some cases it won't use the new driver until the system restarts.

The driver is an interface to a device and is called by services and other applications on your system, these other apps and services may already have an open call to a device that won't be released until your system is rebooted. As a result, a system may potentially be unstable as a result - an app makes a call to a driver and expects behaviour A but the update results in behaviour B and you end up with an application crash or STOP error.

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