why restart?

why is it that some s/w installation require a restart?
i always thought it had something to do with the registry but i can't really see how that fits in now that i give it some thought.

links to a more in depth answer are welcome too :)

If DLL or controls are already in use they can't be replaced on a running system.
In that case some special commands are used to make sure that during a reboot all needed files are replaced.

thanks for that! makes sense.

just thought of something else.

[discussion mode : on]

if dll's are replaced, then what happens during an uninstall?
there have been times where i've tried some software and removed it again because i didn't like the way it was running.

if the problems lie in the dll's, then uninstalling isn't going to resolve the problem - or is it?

When a dll is a shared dll then each program using it will register itself for this dll.
If the last program using this dll is removed then the dll will be removed too, unless it's a system dll.

Although basdewaard is right. If an installation upgrades a DLL and is then uninstalled then the corrupted DLL is not replaced with the original one.