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Thanks, that's a good start. It seems that perhaps the surface of the disk is not physically altered when partitioned or formatted. All these processes do is change some information in a special "control area" of the disk (MBR and/or Partition table?).
I reformatted a 250GB external HD the other day in NTFS. This took a very long time. That's what made me think formatting actually visits each and every "sector(?)" on the HD in the partition being formatted and physically changes it in some way.