SSD power-on hours

Power-on hours (POH) are the cumulative amount of time an SSD’s firmware records that the drive has been powered. The value comes from the drive’s SMART table and accumulates across the device’s life (or since the vendor’s firmware counter started). POH measures powered time only — it does not count how much data was written or how intensively the NAND was used while powered.

How POH is represented and why tools differ

Manufacturers expose POH as a SMART attribute but use vendor-specific raw units: some controllers report true hours, others report half-hours, deci-hours, or opaque counters. Diagnostic utilities may convert the raw value differently, so two tools can show slightly different numbers for the same drive.

Because of vendor and tool differences, treat POH as an approximate powered-time indicator. If exact hours matter when evaluating a used laptop, capture the raw SMART output along with the utility name and version so you can cross-check conversions later.

What POH reliably tells you

POH is a straightforward indication of how long a drive has been in service under power and is especially useful when the device’s purchase or usage history is unknown. It helps estimate age in operational time but must be interpreted with other metrics to assess wear.

Used together with SMART fields such as total host writes (Total_LBAs_Written or manufacturer TBW equivalents), spare-block consumption, reallocated sectors, and media error counts, POH helps form a practical picture of the SSD’s remaining life.

What POH does not show

POH cannot reveal workload intensity: two drives with identical POH might have vastly different write volumes depending on usage patterns (server, video editing, or casual browsing). POH also does not measure throughput, error trends over time, or instantaneous health.

POH alone cannot predict sudden failure. Drives can fail for firmware, controller, electrical, or mechanical reasons that are unrelated to accumulated powered hours; always combine POH with the rest of the SMART report and functional tests.

How to check POH on a laptop — step-by-step

Windows: run a SMART reader such as CrystalDiskInfo or your SSD maker’s toolbox and look for an attribute labelled Power-On Hours or Power_On_Hours. Many vendor utilities also show the same value alongside other health indicators.

Linux and macOS: use smartctl from the smartmontools package (smartctl -a /dev/… ) to print the SMART table including the POH attribute. When inspecting a used laptop, booting a live USB with smartctl or running a light Windows diagnostic lets you capture the full SMART table — include total host writes and wear/spare-block fields in your screenshots.

How to interpret POH with concrete checks

Always read POH together with total bytes written and spare-block or wear percentage fields. For example, a drive with modest POH but very high total written bytes suggests intensive write workloads and higher NAND wear than the POH alone implies.

If POH is high but total writes and reallocations are low and there are no media or read/write errors, the drive can still be appropriate for general laptop use. If reallocations, rising error counts, or large total-write numbers appear, treat the drive as higher risk and prioritise data backups.

Practical decision rules when buying a used laptop

Do not use absolute POH cutoffs alone. Combine POH with SMART wear metrics: low POH + low writes → likely safe for everyday tasks; low POH + high writes → endurance diminished; high POH + healthy SMART fields → may still be fine for general use.

Ask sellers for a screenshot of the full SMART table (including POH, total host writes, reallocated sectors, and any vendor wear percentages). If you can run diagnostics in person, capture the output and keep it with the listing as evidence of condition.