Almost every EIDE or SATA hard disk includes S.M.A.R.T. data. That information is collected by the drive itself and contains data that the manufacturer considered relevant to check reliability. The data is made up of several attributes that have a current value, a worst one, a threshold, some raw data, and some flags. Basically, when any attribute's current value is below its threshold, the hard disk is considered unreliable and likely to fail. By using several techniques, this report tries to give a wider range of info, basing its analysis on advanced comparisons with normal values based on real hard disks and on expert-like checks. The final results are not to be taken as an absolute truth, but they are a very good approach to what a professional would say about your hard disk status.