How can I read out how long a hard disk has been used? I.e. the total number of hours it has been turned on. There is a SMART entry but I don't know how to read it and how to convert SMART values into human-readable time units.
On easy way may be to download and run some diagnostic tools supplied free by the disk's manufacturer. Seagate's Seatools package, for example, has one tool that simply reads all the SMART data and shows it to you in "human" form. WD's Data Lifeguard tools may do the same.