Why do installers often ask you to close all your applications before installing a new software package?   Does it actually matter whether you have open applications when installing new software?

It seems the norm these days is for installers/setup programs to request that you close all open applications before initiating the install process for a piece of new software. I can’t even recall a time it has ever posed a problem.

Well, there a few reasons for this to be historically necessary.  Especially on the Windows platform.  First, installer may require access to registry keys that could be locked by an open program.  Second, the software may install a new Windows DLL, that either could be an upgraded DLL, which could be problematic if there is an application already using the DLL.  Also, without rebooting, it maybe very difficult to force the Windows OS to reload the DLL.

Third, the installer may create a system restore point, and having open programs can cause problems with creating restore points….

Fourth, depending on your web browser, it may not be able to load plugin’s dynamically, for example, try installing Adobe Flashplayer with your web browser open.  With the Macintosh version of Safari, I know can load most plugin’s dynamically, so you don’t have to quit…  But other web browsers may not be able to do this.

Well-written installers will prompt you to close specific applications that are getting in the way. Even some poorly-written installers will give you enough clues to figure out what is in conflict. Just closing applications that you suspect to conflict (web browser while installing a browser plugin) is sufficient most of the time.