What exactly is my computer doing when I format a disk? [duplicate]

Possible Duplicate:
What does Format Do?

I've been formatting all matter of media for years, but I'm unclear on what exactly formatting even is. I know that it prepares the disk to be used and I know that you can format disks in different ways for different purposes and operating systems, but beyond knowing I should use format style ABC for operating system XYZ, I have absolutely no idea what the formatting process actually is.

What does formatting a hard drive actually do to the hard drive? How is a raw and unformatted disk right out of the box different from a hard drive that I've formatted for use? And for that matter, what's the difference between quick format tools that complete the process in seconds versus more in-depth formatting that takes hours on a large disk?

Formatting is necessary to actually store data on a disk. The term is sometimes used interchangably for both low and high level formatting.

Low level formatting is the actual setup of the media with respect to the controller, and hasn't been something that you've had to do manually for over a decade now. Drives come with this already done and most people never need to worry about this.

What you're thinking of is high level formatting. This is the process by which you actually partition and set up the file system of your choice on the drive - it installs the boot sector, file table structure, or whatever the filesystem needs in order to be recognized. Once the file system is in place, software that can read it can utilize it. (Quick format versus long format is purely a question of how the formatting works - quick ones usually just set up the structure and ignore anything else that might be on the disk, while long ones will generally zero out anything that might have been left over from a previous partition).