[juliette salexa]

I'm wondering if anyone here knows the physics behind how information is stored and erased on hard disks.

I've heard that, even tools like KillDisk will not completely erase your hard drive PERMANENTLY. I've heard that all they do is write zeros on top of whatever was there before, for each bit. I've heard that even if you use KillDisk 6 times in a row, a skilled recovery-man can recover your data. I saw on a tech forum a long time ago (can't remember which one) that the only way to PERMANENTLY delete all the information stored on your disk, is to light it on fire (or something to that effect).

Let's start with a hard drive freshly made from the manufacturer. What is PHYSICALLY going on when one begins to 'write' information to that disk, and what is physically going on when one tries to 'erase' that information ??

If the explanation is lengthy, and you know a good article that summarizes the answers to the above questions concisely and accurately ...I'd be glad to read that if it saves you some time replying to me.

I've taken postgraduate electromagnetism and quantum physics courses, so feel free to go as theoretical as you need!

[daniel_b2380]

have you ever disassemblrd a harddrive? - it's the easiest way to learn what is physically present - then applying your education to conceptualize the ensuing electro-physical operations involved


or here are a few link to use to start:

http://www.google.com/

http://www.google.com/support/websea...&answer=134479

this article will help with some of the nomenclature involved:
http://en.wikipedia.org/wiki/Hard_disk_drive

edit:
-OR-
rather than learning about legacy systems - you might apply your time to the newer emerging technology

http://en.wikipedia.org/wiki/Flash_memory
http://www.googleguide.com/

remember, it's 'keywords' which help the most in formulating a google search - so the above links should offer enough explanation to get you started