hard drive - Why erase file with random patterns instead of all 0's or 1's?

Computer files aren't actually removed when they are deleted on Windows. The address pointer is simply released and that space freed for overwrite later.

For sensitive information, it is recommended that you erase it with a scrubber that obscures the file first.

It turns out that these scrubbers write a specific sequence of 1's and 0's to the hard drive over several iterrations.

Why can't you just write all zeros or all ones to the file and then delete it normally?

How could someone manage to recover data from a straight wipe like that any more or less than using multiple iterations and patterns?

Answer

The short version: theoretically, the original pattern can still be read by certain sophisticated hardware and software. To ensure the security of your "erased" data, it must be wiped.

The long answer: http://en.wikipedia.org/wiki/Data_remanence

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Edit: In fairness to those that have already voted, I'm leaving my answer as originally written; however, do read the comments for full disclosure.

Many people, myself included, feel that anything more than one pass with cryptographically-sound pseudorandom data is a waste of time and CPU cycles.