Subject: Re: MIT ChaosNet code port to Linux
From: Erik Naggum <>
Date: Fri, 21 Jun 2002 03:26:32 GMT
Newsgroups: comp.lang.lisp
Message-ID: <>

* Barry Margolin
| Once ASCII became the standard character set, you were pretty much forced
| to use at least 7 bits.

  As far as I can see from the historical record, DEC always used 7-bit ASCII
  on their PDP-10 series operating systems.  I have no record of PDP-6 systems.

| 6-bit ASCII is only usable if you're willing to forego lowercase.

  Actually, there is no such thing as 6-bit ASCII.  SIXBIT has no control codes
  and is completely useless except in extremely well-controlled settings.
  There is no support for printing or typing SIXBIT files, for instance -- if
  files were opened with 6-bit bytes, they would appear to contain 32 control
  codes and the first 32 non-letter ASCII character -- hardly useful.  (Yes, I
  have tried this, back in the summer of 1980, wasting huge amounts of paper
  due to the unfortunate placement of certain control codes.)

| I think it was used in directory files (the filename and filetype were each a
| single word, allowing each component to be up to 6 monocase characters), but
| file contents were generally 7-bit ASCII.

  At least under TOPS-10, the right half of the file type word was used for the
  CFP (compressed file pointer) into the RIB (retrieval information block) in
  the UFD (user-file directory) or SFD (sub-file directory), so you could have
  only three letters in the file type, but six in the file name, thus a
  directory entry was formed by two machine words.  (For completeness, the UFD
  was itself a file with extension .UFD in the MFD (master file directory.))
  [All according to my trusty old TOPS-10 Monitor Calls Manual, Volume 1, from
  February 1984.]

| BTW, I think ASCIZ means "ASCII with Zero-byte terminator", a la C strings.


| Multics, another 36-bit system, also used 9-bit characters.  But since
| ASCII was only 7 bits, this wasted much more than ITS's 7-bit characters: 2
| bits/character versus 7 bits/5 characters, or 25% more words used to hold
| the same number of characters.  In the days when memory (both physical and
| virtual) was extremely expensive, this could make a big difference.

  I did not follow that computation, but the number of words to hold a file of
  9-bit characters (four to a word) compared to 7-bit characters (five to a
  word) would indeed be (/ 1/4 1/5) => 5/4 or 25% more.
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