First off, it's not true that simply deleting files/programs and then high level reformatting wipes the hard drive of data, it does not. The Master File Table (MFT) is a table of contents, when one deletes files/programs, it simply deletes the entry in the MFT, not the data on the pages (cylinders, sectors, blocks), that the MFT refers to, such that those areas are merely available, if required, for new data. There is another problem. Since these cylinders are oh so narrow, there are deviance's left and right of center, due to natural vibrations, whose position varies with each full rotation, that some call layers, but layers are actually only to be found on dual layer optical disks, not HD's, anyway this is why the US DOD utilizes a 7 pass wipe, by writing 7 various data patterns, which is enough to account for these deviations of head centering. So to ensure no data from a previous install is present on the disks surface, one must low level format at least 7 times, at least to be as sure as the US DOD that the drive is totally clear, then high level format, and reinstall your OS of choice, and other supporting programs. Better yet, after doing this once, create a clone (ghost) of a freshly installed OS, prior to any use, so that this procedure can be accomplished quicker, if need be. But the 7 pass low level format is required every time to be sure, no remnants are left over from previous installs. Actually if it's not a matter of security, you can fore-go the low level format, and instead boot with a pre-install environment optical drive that has the capability of formatting HD's to another file system, like FAT 32 (note there are some partition size limitations), and simply copy data to the entire drive/partition once, I use 1 gig vob files, so as to do it quickly, then reformatting with, I assume, NTFS and going ahead with the install of the OS. These are the most sure methods to ensure that previous installs can't "bleed" through your new install.
