PUNCH A HOLE IN A DOUBLE-DENSITY TO MAKE A HIGH-DENSITY? 
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       Yes, but I certainly wouldn't trust any data I intended to keep 
  for more than the next minute or two to such a diskette.  The extra 
  hole is not the only difference between a double-density and a 
  high-density disk.  The magnetic media on a high-density disk 
  is a different type that is much more susceptible to formatting.  
  Double-density diskettes should only be formatted as 800K.  With the 
  plummeting prices of real high-density disks, this really shouldn't 
  be an issue anymore.