Power-on hours (POH) is the length of time, usually in hours, that electrical power is applied to a device. A part of the S.M.A.R.T. attributes (originally known as IntelliSafe, before its introduction to the public domain on 12 May 1995, by the computer hardware and software company

Compaq Compaq Computer Corporation was an American information technology, information technology company founded in 1982 that developed, sold, and supported computers and related products and services. Compaq produced some of the first IBM PC compati ...

), It is used to predict drive failure, supported from almost all

Hard Drives A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magnet ...

and SSds. Power-on hours is intended to indicate a remaining lifetime prediction for hard drives and

solid state drive A solid-state drive (SSD) is a type of solid-state storage device that uses Integrated circuit, integrated circuits to store data persistence (computer science), persistently. It is sometimes called semiconductor storage device, solid-stat ...

s, generally, "the total expected life-time of a hard disk is 5 years" or 43,800 hours of constant use. Typically, after a disk reaches 5 years or 43,800 hours of power-on time, it is no longer in perfect condition and therefore is more likely to fail. However, some older and newer devices can still work perfectly fine even after. Some devices have even reached more than 10 years of power-on time without showing any problems or errors. Google tested over 100,000 consumer grade serial and parallel ATA hard disks, finding evidence that S.M.A.R.T. attributes like POH played a heavy role in device failures.

References

Survival analysis Reliability analysis {{electronics-stub