Yaskawa YASNAC PC NC Maintenance Manual - Manual (Page 239)

PC NC Maintenance Manual Chapter 8: Fixed File Operations
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10. Select Delete Partition(s) from the Tools menu.
11. The current hard disk partitions are shown. All of these partitions
must be deleted, and the PC NC hard disk image is to be cleared.
Before executing this procedure, ensure there are backup copies
of all CNC program files.
12. Check ‘C: Drive’ and click the Delete button.