Power-on hours
{{Short description|The length of time that electrical power is applied to a device}}
{{Use dmy dates|date=September 2023}}
Power-on hours (POH) is the length of time, usually in hours,{{Cite web|url=https://www.z-a-recovery.com/manual/smart.aspx|title=ZAR - Quick guide to understanding S.M.A.R.T. information|website=www.z-a-recovery.com|quote=...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...}} 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),{{Cite press release |url=http://www.seagate.com/newsinfo/docs/disc/enhanced_smart.pdf |title=The Emergence of Reliability-Prediction Technology |date=2001-06-12|access-date=2018-02-01 |archiveurl=https://web.archive.org/web/20010612122823/http://www.seagate.com/newsinfo/docs/disc/enhanced_smart.pdf|archivedate=2001-06-12}}
It is used to predict drive failure, supported from almost all Hard Drives and SSds.
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" {{Cite web|url=https://kb.acronis.com/content/9109|title=S.M.A.R.T. Attribute: Power-On Hours (POH) | Knowledge Base|website=kb.acronis.com}} or 43,800 hours of constant use.{{Cite web|url=https://www.hdsentinel.com/help/en/54_pot.html|title=Power on time|website=www.hdsentinel.com}}{{Cite news |last=Hepworth |first=Shelley |date=2022-02-11 |title=Most hard drives have a lifespan of three to five years. Have you checked yours lately? |url=https://www.theguardian.com/technology/2022/feb/12/most-hard-drives-have-a-lifespan-of-three-to-five-years-have-you-checked-yours-lately |access-date=2024-08-03 |work=The Guardian |language=en-GB |issn=0261-3077}}
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.{{Cite web |title=Facebook |url=https://www.facebook.com/photo/?fbid=3814292722032664&set=a.157734857688487 |access-date=2024-08-03 |website=www.facebook.com}}
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.{{Cite journal|last1=Pinheiro|first1=Eduardo|last2=Weber|first2=Wolf-Dietrich|last3=Barroso|first3=Luiz André|date=2007|title=Failure Trends in a Large Disk Drive Population|pages=17–29 |url=https://research.google.com/pubs/pub32774.html|language=en}}