theU.S. National Institute of Standards and Technology (NIST), in itsGuidelines for Media Sanitization of 2006 (PDF), stated that “for ATA disk drives manufactured after 2001 (over 15 GB) clearing by overwriting the mediaonceis adequate to protect the media.” When NIST revised its guidelines in late 2014, it reaffirmed that stance.NIST 800-88, Rev. 1 (PDF)states, “For storage devices containingmagneticmedia, a single overwrite pass with a fixed pattern such as binary zeros typically hinders recovery of data even if state of the art laboratory techniques are applied to attempt to retrieve the data.” (It noted, however, that hidden areas of the drive should also be addressed.)

For ATA hard disk drives and SCSI hard disk drives specifically, NIST states, “The Clear pattern should be at least a single write pass with a fixed data value, such as all zeros. Multiple write passes or more complex values may optionally be used.”

Even for Purge, one pass will suffice, it said, though an inverted three-pass method is also an option.