Permissons are the bit flags that are used by the operating system to determine which users have access to what files and directories. They also indicate what type of action users can take upon files and directories.



every file and directory on your osx box has an owner, a group and set of permissions.



if you go to the terminal and do ls -a , for each file and directory you will see something like this:



-rwx-rw--r-- 1 killy staff 0 Jun 6 15:00 babyprogram



what this cryptic shit means is that:





killy is the owner of the file called babyprogram


staff is the group to which the babyprogram belongs


-rwx-rw--r-- are the permissions set for this file. They are divided into 3 parts: the 'user' permissions, the 'group' permissions and the 'other' permissions.





the first part rwx means that the owner of the directory (killy) can read and write and execute the file.


the second part rw- means that users of the group (staff) can read and write but not executethe file.


the third part r-- means that all other users can only read the file.






so with permissions you can restrict access to different files and directories on your system. this is not so useful on a single user machine, but the utility is pretty apparent on a multi-user system. on your imac, for example, permissions are a useful way to prevent you from fucking up important files and directories. you will notice that important System directories and files are not owned by killy, but by a user called root. if you try to manipulate a file owned by root you may find that the permissions set for the file will not allow you to save the changes.





as to why exactly you need to run the Fix Permissions utility to get imovie to run more smoothly I am not sure...