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Specifically, I am long-formatting to ExFAT.

Is this filling my external HDD with zeros?
If not, how can I do this with a 230GB SATA hard drive in an external USB caddy?

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up vote 4 down vote accepted

If you're running Windows Vista or newer, then yes.

That KB article details the changes with the format command starting with Vista, a long format now writes zeros to the entire drive. Previous versions did a read only check of every sector.

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I have always wondered if it only writes zero's when using the command prompt, I cannot find documentation where it says it does overwrite when formatting in explorer, disk management or from an Vista or W7 install dvd. The document specifically shows it done from the command prompt and using diskpart. – Moab Feb 25 '12 at 17:30
@Moab: I'd guess that the underlying system calls are the same from cli and gui, so it doesn't matter. – afrazier Feb 25 '12 at 18:26
I don't like assumptions even when they are obvious, I guess I will test it soon. – Moab Feb 25 '12 at 18:31
With ImDisk and some small in memory volumes, it should be relatively easy to test. – afrazier Feb 25 '12 at 18:41
I have a small utility to watch the read writes on any drive in my system, so I will just connect a small usb hard drive and long format it. – Moab Feb 25 '12 at 18:45

For Windows XP, No, the "long" or "regular" format is just checking the sectors for consistency. When the files get erased, only the file tables are erased. The files remains are still recoverable with unerase file utilities. Here's Microsoft's explanation. What you want to use is a utility that performs a "kill disk". One good tool that has a 1 pass freeware version is Active@, but there are many others if you do a search. (1 pass means it writes 0's to each sector making those file remains.) Writing over USB to a 230gb drive will take many hours and is an overnight task.

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