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.
Macfax Premium reports include the SSD's power-on hours, total host writes, percentage used (where the vendor reports it), and the model identifier. Reports also flag any SMART warning conditions reported by the drive.
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