Power-on hours

From HandWiki
Short description: The length of time that electrical power is applied to a device

Power-on hours (POH) is the length of time, usually in hours,[1] 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),[2]

It is used to predict drive failure, supported by manufacturers such as Samsung, Seagate, Toshiba, IBM (Hitachi), Fujitsu, Maxtor, Kingston and Western Digital.[citation needed]

Power-on hours is intended to indicate a remaining lifetime prediction for hard drives and solid state drives, generally, "the total expected life-time of a hard disk is 5 years" [3] or 43,800 hours of constant use.[4]

Once a drive has surpassed the 43,800 hour mark, it may no longer be classed as in "perfect condition".[citation needed]

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.[5]


  1. "ZAR - Quick guide to understanding S.M.A.R.T. information". https://www.z-a-recovery.com/manual/smart.aspx. "...the raw value of the attribute is stored using all sorts of measurement units (hours, half-hours, or ten-minute intervals to name a few) depending on the manufacturer..." 
  2. "The Emergence of Reliability-Prediction Technology" (PDF) (Press release). 2001-06-12. Archived from the original (PDF) on 2001-06-12. Retrieved 2018-02-01.
  3. "S.M.A.R.T. Attribute: Power-On Hours (POH) | Knowledge Base". https://kb.acronis.com/content/9109. 
  4. "Power on time". https://www.hdsentinel.com/help/en/54_pot.html. 
  5. Pinheiro, Eduardo; Weber, Wolf-Dietrich; Barroso, Luiz André (2007) (in en). Failure Trends in a Large Disk Drive Population. pp. 17–29. https://research.google.com/pubs/pub32774.html.