SSD wear
A measure of how much of a Mac's solid-state drive has been written to relative to its rated lifespan; high wear correlates with reduced reliability.
Modern SSDs have a finite write endurance, expressed in TBW (terabytes written) or as a percentage of remaining life. macOS exposes SMART (Self-Monitoring, Analysis, and Reporting Technology) data that tracks total host writes, power-on hours, and a vendor-specific 'percentage used' or 'available spare' metric for every internal SSD.
SSD wear is meaningful for high-end Macs (Mac Studio, MacBook Pro) running ML training, video editing, or other heavy-write workloads. A Mac Studio with 100 TB written may have plenty of life left; a Mac Studio with 800 TB written may be approaching the end of its rated endurance.
Listings rarely surface this. A seller can quote 'lightly used' without revealing that the drive has 50,000 power-on hours and 500 TB written. Buyers paying high-end prices for high-write workloads should always ask.
Every Macfax report, free Basic included, reads the drive's own wear counters where the controller exposes them, and flags any SMART warning condition. Not every Mac reports the full set, so a report shows what its drive actually returned rather than a fixed list.
See it on a real Macfax report.
Free Basic report in under a minute. Identity, authenticity, spec match. Every check lands on the report, signed.