Even more insidious are the methods of reading how strongly the magnetized bit is positive or negative. If the bit is on, but not as strongly as others, it might have been off before getting flipped. If very strongly on it might have been reinforced when the 1 bit was written to it. It would take several passes of randomized ones and zeros to fool this technology.
Ken Klein Sr. Systems Programmer Kentucky Farm Bureau Insurance - Louisville kenneth.kl...@kyfb.com 502-495-5000 x7011 -----Original Message----- From: IBM Mainframe Discussion List [mailto:ibm-m...@bama.ua.edu] On Behalf Of Gerhard Postpischil Sent: Thursday, July 02, 2009 5:29 PM To: IBM-MAIN@bama.ua.edu Subject: Re: ERASEDATA - DASD disposal Eric Bielefeld wrote: > I always wondered if it was possible to read data if binary zeros or > some other pattern were written to the disk. I thought that it would > be very hard, which the article quoted seemed to agree with. But > then, I noticed that the writer of the article didn't sign his name. As I understand it, the magnetized portion of a track is slightly wider than the write head. When a track is rewritten, the head alignment will be slightly different, leaving a little bit of the original track. So what you are writing on subsequent passes doesn't really matter, unless you do it often enough to make it unlikely to retain any trace of the original. And of course there are the newfangled storage boxes where you get a different physical track on every write..... Gerhard Postpischil Bradford, VT ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
