Library question....

There are three - all of them necessary.

The ~/Library (in /Users/<username>) folder contains user specific settings, data, and other support files which could be unique to the user.

The /Library and /System/Library are required by the OS and should normally be left alone.

 

I think there are four, assuming only one account, but I can't check right now.

 

Nope, the other poster had it right. Only three on a standard single-user computer.

Of course, if there were more, they should also be left alone. So this is really not important to the topic at hand.

jW

 

Ok, I'll take your word for it. No sense searching for something that's not there!

 

To add a bit more detail, for reference, the top-level /Library folder contains settings and shared components (such as fonts on System Preference panels) that are available to all users, while the /System/Library folder contains such things that are an integral part of the OS.

You don't want to mess with any of them if you don't know what you're doing, but as a general rule things added to the user's ~/Library are available to that individual user only, while the top-level /Library folder is very similar, but the components stored in there are for everybody. /System/Library, in turn, is ONLY for things Apple installs, and will never be messed with by the user.

To use preference panes as an example, if you wanted to install a preference pane for just a single user, you would put it in ~/Library/PreferencePanes. If you wanted to install it for all users of the computer (usually the case), you would put it in /Library/PreferencePanes. (The system will actually ask you this when you go to install a new preference pane.) All the default system preferences that Apple builds into the OS are in /System/Library, and you would never, under any circumstance, mess with its contents.

Likewise, if you're uninstalling something (like a font or Preference pane), it's ok to delete it from either /Library or ~/Library, but if you delete something from /System/Library you could well break the OS.