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In Linux, the --type a option in od is explained as

--type=
      Select the format in which to output the file data
…
a
     named character, ignoring high-order bit
…
Only the least significant seven bits of each byte is used; the high-order bit is ignored.

Now this answer here explains a lot, especially "and words were two bytes long" – which leads to my specific

Question: What does high-order bit mean in connection with "named characters"

Maybe I'm just missing something…

Community
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erch
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1 Answers1

2

"Named characters" means the output will print the name of a character rather than its numerical ASCII value. For printable characters, the name used is the actual character and for non-printable the names are things like nl for newlines and sp for spaces.

The high-order bit is the bit with the highest value. For single-byte ASCII characters, this bit is the 8th bit whose unsigned value would be 128. If you ignore this bit, you are left with ASCII values between 0 and 127 and it is from this range that od is picking the name of a character.

casey
  • 14,754
  • Great and very helpful answer. Where did you find this information? (still a Noob trying to figure out stuff myself but often ending frustrated…) – erch Feb 17 '14 at 23:18