You can't hook a laptop drive up directly to a desktop PC, the pins are different. You would need an adaptor for that.
And laptop drives have a special hazard:
You must be careful to properly orient the laptop drive to its connection, if you use an external enclosure or a direct 3.5" to 2.5" adaptor. Laptop connector pins don't have any safety guide (such as pins missing, or notches for the connector) to indicate how the connectors are oriented; it's just got two rows of pins, and two of those pins are the power connections--there isn't a separate connection for power cables. It is possible to attach the cable upside down. If you do that and power it up, you fry both the drive and the computer's mobo. If you get an external enclosure this shouldn't be a problem--but it is easy to do wrong if you buy a laptop-to-desktop drive adaptor.
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To wipe the drive, there are a bunch of programs you can use. I like Eraser: http://www.heidi.ie/eraser/
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Also note: laptop drives tend to run slow compared to desktop hard-drives.
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Also I would agree: retail walk-in stores tend to overcharge drastically for this kind of stuff. Order it offline if you can, you'll get a better selection and pay a much lower price. Many items like cables for example cost 2-3+ times as much in local retailers as they do online.
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