I would like to understand what does formatting really remove.
When launching a computer, something shows up, resembling DOS. This can't possibly be stored on a hard drive ? Where is it stored then ?
I read that there is a boot sector on the hard drive, is there some leftover on the hard drive after formatting it ? Does it really ends up with 0 bytes left on a drive ?
Best Answer
That's really three different questions, with a long, hard road to full understanding.
Let me try to compress that into smaller, simpler ideas...
Think of a hard drive like a reference book with an index at the back to quickly look up relevant sections. Then remove the index. The book is still readable, but only in a more linear fashion. It's harder to find the right chapter, but not impossible.
If you quick format a drive, all you are really doing is removing the 'index' - all the actual data is still there. At this point, if anything were to try to write to the disk, it wouldn't 'know' the old data was there & so would build a new 'index' & write over any old data.
A full format would overwrite the actual data itself - though it may still be recoverable with advanced techniques.
When you boot a computer with a wiped or totally blank hard drive, what you see is a tiny operating system (actually a standalone program, but it acts like a small OS, to all intents & purposes) that is kept in the actual computer hardware, not on the hard drive itself - which just tells the machine where to look next for instructions.
The boot sector is a small sector of the hard drive that contains an instruction telling the computer where to look next for a fully bootable system.