At 03:41 PM 4/21/02 -0700, Mr Babak Memari wrote the following: >But how is it possible to recover data after Formatting data from hard disks? >Can you give me basic information about it?
Imagine a hard disk drive as a series of concentric circles called tracks that we then stretch out so they looks like a series of highways. Then looking at any one "highway" we could see that it contains magnetized or demagnetized areas that we define to be data. This data needs an index to where it begins and ends on each track or highway. This is called the file allocation table or FAT. If the format command only destroys (formats) the FAT, the data is still exactly as is on each track and only the index is missing. So data could be recovered easily. This is the typical step that most "un-delete" programs follow, they simply "redo" the FAT for the particular data (file) that was formatted or deleted. Well lets say that you actually want to "destroy" the data that is on a track, what do you do? You must write something over the existing data, commonly zeros or some such character. Because of residual magnetism even this isn't totally effective, that is the original data can still be "read" from under the zeros using high powered magnification and other techniques. To effectively remove all possible traces of existing data requires a series of writes over the same data area. Special "wiping" programs do this from 3 to 35 times or more. NOTE: low-level formatting is more secure than a plain format but still is not not secure enough. Data can still be recovered. For example, see http://www.commoncomputers.com/ Secure Deletion of Data from Magnetic and Solid-State Memory (a must read!) http://www.safedelete.com/a-gutmann.phtml DoD 5220.22-M National Industrial Security Program Operating Manual (NISPOM) http://www.dss.mil/isec/nispom.htm DoD Trusted Computer System Evaluation Criteria http://www.radium.ncsc.mil/tpep/library/rainbow/5200.28-STD.html -- Gerry Boyd ============= PCWorks Mailing List ================= Don't see your post? Check our posting guidelines & make sure you've followed proper posting procedures, http://pcworkers.com/rules.htm Contact list owner <[EMAIL PROTECTED]> Unsubscribing and other changes: http://pcworkers.com =====================================================
