Tech Talk

Mac Format - - MAC SOS - by Luis Villazon

The other day, I was eras­ing the hard disk of an old iMac, prior to sell­ing it. It has a blown graph­ics card, so it doesn’t boot any­more. I was sell­ing it for parts (even a dead iMac is still worth about £70 to £80 for its screen) so I wasn’t plan­ning to re­in­stall OS X. I just wanted to take my data off the disk first. So I con­nected it with a FireWire ca­ble to a Mac mini, booted it in Tar­get Disk Mode, and then used Disk Util­ity to per­form the min­i­mum, one-pass se­cure erase to over­write it with ze­ros.

While that was run­ning, a friend popped round for cof­fee and asked what I was do­ing. He sucked through his teeth when I ex­plained. “One pass isn’t go­ing to be enough for that”, he said. Which is rub­bish. Try ring­ing a spe­cial­ist data re­cov­ery firm like Kroll On­track and see what they will charge to re­cover data from a disk that has been wiped with one-pass erase. It won’t even quote you. Multi-pass over­writes with ran­dom data ex­ist be­cause ev­ery­one be­lieves that you can never be too care­ful – but you ab­so­lutely can. Peter Gut­mann, who wrote a 1996 pa­per sug­gest­ing that a mag­netic force mi­cro­scope could re­cover over­writ­ten data says this would not work on to­day’s drives. Even the one-pass erase took al­most three hours on my iMac. A seven-pass erase is a waste of time and elec­tric­ity and just turns your data from ‘un­re­cov­er­able’ to ‘still un­re­cov­er­able’. In the past, Luis Villazon has re­moved old hard drives and phys­i­cally driven a nail through them.

Ev­ery­one be­lieves that you can never be too care­ful – but you

ab­so­lutely can

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