Zach is absolutely right.  A drive is just a collection of bytes -- billions and billions of them.  Formatting read and writes to some of those bytes.  It doesn't do anything special that doesn't happen during an ordinary read/write operation.
When you type FORMAT C:, all you are doing is telling DOS that you would like to erase the FAT (File Allocation Table) on the C: drive.  DOS finds the correct partition and drive, and wipes the FAT, creating a new table.  Then, as you watch the 1%. . . 2%. . . 3%. . . counter, FORMAT is testing the data area of the drive by reading or writing to every single cluster (sector).  Again, the FAT, the partition tables, the data area -- these are all just artifical structures on the hard drive, created by the operating system and not treated any differently by the drive hardware itself.  In fact, the hard drive doesn't even "know" it's being formatted.  As far as it's concerned, some one is just reading and writing to the disk as usuall.
So-called "low level formatting" (not the kind done at the factory which is a different process altogether) is not much different.  When you low level format a hard drive using a special utility, it simply ignores partion tables, FAT's, data, boot sectors and every other artifical structure created by an operating system and writes zeros to the entire drive.
Modus