The AutoExec.Bat, Config.Sys and other startup files contain information about various drivers and other programs that need to be loaded into the memory when the computer starts, i.e. before you can start using the computer for your normal work.

Whenever a program installs any software that needs to be loaded into the memory right when the computer starts, it edits one of the appropriate startup files and places an entry for this software in it. Since your computer is running at the time this software was installed, the software has not been loaded into the memory. In order for this to happen you need to restart the computer, so that the new entry in the startup file is executed.

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