Reformatting hard drive

I would like to reformat the hard drive of my Studio 17 1747 laptop. Before i do so, i was just wondering how i will be able to reinstall my operating system (windows 7) if i don't have a disc for it. I purchased my computer from Dell, but did not receive a disc with which to reinstall windows 7. Windows 7 came preinstalled on my computer from the factory. I did however receive a disc called "Dell Drivers and Utilities" (already installed on your computer), does this disc have the operating system files on it as well, or do i need to obtain a disc with the operating system files on it, before i can successfully reformat my hard drive and reinstall my operating system?