HDHacker is a tiny portable tool which can read, display, save and restore a drive's master boot record, boot sector, or just a defined number of continuous sectors (1-16). (Beware the "restore" option - make a mistake and it could trash your system.)
At a minimum, this is a useful way to find out more about a drive (you can check its file system, confirm that the sectors haven't been completely overwritten). You can also back up your chosen sectors, allowing them to be restored later if they're corrupted (although if your system drive is damaged you'll need some other bootable environment to launch the program).
The HDHacker interface is very basic, just as you'd expect for a 112KB executable which still runs on anything from Windows NT up.
You're able to choose your preferred drive - logical or physical - from a list.
Next, you must choose a starting sector (#1 for the boot) and the number of sectors to read.
Click "Read sector..." and HDHacker reads and displays your chosen sectors. Most of this will be meaningless binary garbage, but there may also be useful information (if the sector starts with ".RNTFS" then you'll know this is an NTFS drive, for example).
There are also buttons to save sectors to files, reload them, and write sectors to disk. BEWARE: if you use the "write" option and accidentally choose the wrong sector or disk then your system could become unbootable. Even if you know what you're doing, don't touch this unless you've a full system backup to hand.
HDHacker provides an easy way to view, back up and restore drive sectors. This might be a problem, though, as if used incorrectly you could very easily make a drive unreadable. Use with extreme caution, if at all.