I need to reformat my iMac, do i need to use disks or can i format it thorough the system????????
Assuming you are trying to reformat your startup disk (probably the only disk you have on your iMac), then yes, you will need a system install DVD. Either the one that came with your computer or an operating system DVD that you purchased later.
You need to use the original DVD that came with your computer. http://support.apple.com/kb/HT3910
Why do you need to reformat? It's not usually necessary to do so if you have an isuue.
To answer your question, yes you will need to run the installer disk.
Retrieving data ...