I just took blackframe and super-overexposed white wall images at ISOs
800, 1600, and 3200 on my 10D. I converted them all to uncompressed DNG
files, and looked at the RAW data in a hex editor (set to look at the
data as decimal numbers, assuming 16-bit unsigned data). The data
patterns are the same for the 1600 and 3200, and both are a little
strange. You get a long string of even numbers, then a long string of
perfectly alternating odd and even numbers, then a long string of odd
numbers, then a long string of alternating numbers again. ...