The trick isn't using /dev/zero, the trick is using the seek parameter. The dd command skips nearly 8 GiB into a newly created file and writes something there. This creates a file that is 8 GiB large, but with no data (not zero, just nothing at all) in the first 8191 MiB. Therefore, the system doesn't actually write anything there, and doesn't even allocate the storage. If you read from these blocks, you will get generated zeros. This is called a sparse file.

I have a hotkey that launches an xterm with octave in it.
(Octave is a mostly MatLab compatible numeric computation language: http://www.gnu.org/software/octave/index.html

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