HDD S.M.A.R.T. extension controls the health status of your hard disks. It can discover a probable hard disk drive (HDD) fail before it actually occurs. HDD S.M.A.R.T. extension uses S.M.A.R.T. technology, included in all modern hard disks.

S.M.A.R.T. is a self-testing and monitoring performed by some HDD. It looks like the HDD is continuously making self-tests and calculating some "attributes", which reflect the current state of efficiency and status of the HDD.
Each attribute means some detail in HDD status Ö total hours of work, count of read errors, and others. If after a self-test, the HDD "thinks" that its state is changed, it changes the value of the corresponding attribute. For example, if the time of spin-up from idle state changed, the HDD would change (lower) the value of the "Spin-Up Time" attribute.

Each attribute has a threshold (lower) value and, at achievement, the HDD may stop working. HDD S.M.A.R.T. extension monitors attribute changes and reports the changed values.