Well, it takes a llittle bit to explain.
In previous versions of CUCM, they only have "Save" button on the admin page. As the name indicated, "Save" button saves configuration into database (hard disk).
However, saving configuraton to hard disk may or may not have immediate effect on the system functions. That's because most processes (programs) making decisions based on the data in computer memory (RAM).
Changing the data on hard drive does not necessary update the memory immeditately. There's a mechanism called "Change Notification" to ensure the update. The "Apply Config" button is a manual method to make changes take effect immediately.
Guess it's as clear as mud?
Michael
