Hard disks

The hard disks inside computers have one or more physical disks. The read/write head which is flying above this disk performs all read, write, delete operations.

As hard disk capacity increases, the data is stored on smaller and smaller areas on the disk surface. Any small (even microscopic) damage or dirt on the surface would highly reduce the chances to access important data. The disks are hermetically closed to keep the humidity and dirt outside the disk chassis.

This process is not always completed without problems. It is possible that some areas of the disk surface is not readable or writable because of a small damage or dirt. In this case, the hard disk marks this area as bad and it will never use these sectors again for any (read or write) operation. If this area previously had data, the hard disk tries to read and copy the data to a special spare area first. After the process is completed, all access to the old area will be redirected to the spare area. The original (problematic) area of the disk cannot be accessed even after a complete reformat.

It sounds good – because the problem is automatically solved but the user will not notice anything about the constantly decreasing hard disk status until he will need to face an unusable hard disk and data loss.

There are other possible problems can degrade the hard disk condition. High temperature, incorrect power or mechanical shock, vibration can seriously damage the hard disk. Many of such problems can be detected by using Hard Disk Sentinel and the data loss caused by the problems can be avoided.


S.M.A.R.T. (Self-Monitoring Analysis and Reporting Technology) is introduced by IBM. It was created to monitor the disk status by using various methods and devices. A single ATA hard disk may have up to 30 such measured values (attributes). Some of them directly or indirectly affect hard disk health status and others have statistical information.

Today all modern IDE/Serial ATA/SCSI hard disk have S.M.A.R.T. feature. It is not really a standard – so the meaning of the attributes may be different from manufacturer to manufacturer. Because of this, a manufacturer-independent disk health analysing method is neccessary to determine the real status of any hard disk. Hard Disk Sentinel can do this, please see the condition calculation methods section.

Many attributes are used by all manufacturers and they are used in the same (or near same) way. That’s why for example it is possible to detect the temperature and the power on time of many hard disks. These values (and many others) are monitored by this application.

According the S.M.A.R.T. specifications, when a problem is detected, the hard disk should work for at least 24 hours to perform the data backup. But in many cases this time is not enough – that’s why it is important to recognize problems and prepare before it’s too late.

Note: some hard disk controllers or drivers may prevent the reading and examining of S.M.A.R.T. values. In these cases, the current health, temperature or other status cannot be determined for the affected hard disk(s). Please contact the manufacturer of the controller for an updated driver or firmware. It is not possible to determine the S.M.A.R.T. status of external USB/Firewire hard disks and hardware RAID arrays.

Hard disks, S.M.A.R.T.