What does formatting do?

[meredith101]

I formatted a drive to reinstall windows to sell my PC. And............................SHOCK!!!!!!!!!!! there is still old data there, if I use an undeletion tool!!!!!!!!!!!!!!!
wow!!!!!!!!!
I thought formatting really wiped it?????????????

[ryepie]

High-level formatting does not destroy the data on the disk, Windows (or DOS) only erases the records of where the files are, not the actual contents of the files themselves, much like if you ripped out an index from a book - you can still find what you're after it just takes a bit more effort.

The reason why Windows operates this way is that if you really want to securely remove data from a disk then you have to write random data (or zeroes) across the entire disk platter, basically recording over the old data, and this can take some time, especially as some goverment standards require you to repeat the process multiple times. Now most regular users don't want to sit around for hours waiting for a disk to be securely 'erased' when they format a drive.

If you are concerned, I would recommend the excellent SDelete written by a chap who is pretty much an guru on all things windows. He is now employed by microsoft but his tools are still available FOC from MS http://www.microsoft.com/technet/sysinternals/ Security/SDelete.mspx

Even after all this it apparently is still possible to retrieve some data using extremely sophisticated and expensive equipment. That's why most organisations will also physically destroy a disk as well!

[meredith101]

great answer thanks rypie!
I heard something about 'magnetic footprint' or suchlike (I know a hard drive's info is already magnetic, but even after overwrite the disk is different from a new one).....

[ACtheTROLL]

Another respected option is eraser (the hint is in the name!)
http://www.heidi.ie/eraser/download.php
see the faq
http://www.heidi.ie/eraser/faq.php#erase hd

There is almost no way to completely erase your data
but I tend to install eraser .... erase my very personal details with the 35 pass option on docs and settings and the windows directory (in dos)

then 7 pass on stuff I don't realy care about.

still takes for ever ...

[ryepie]

Yes Meredith, you are correct about the magnetic footprint; and the application of a electron tunnelling microscope can retrieve data that has been written over many many times.

Another technique of data elimination is degaussing. where a strong magnetic field is applied to the entire disk, and is more secure than overwriting.

The 35 pass option that AC has is known as the Peter Gutman method and is the most secure, known about, method of file overwriting.

I just looked it up and the american DoD recommends a 7 pass file overwite using a particular algorithm for anything up to Secret. Anything that is Top Secret is degaussed and then physically destroyed - one example I saw was the disk platter was put into a chipper, then melted down into slag, then put through the chipper again!

[meredith101]

Yeah, just in case someone wanted to run 'Undelete' on the slag..........:)