NWG/RFC #373 14 July 1972
NIC 11058 SU-AI
ARBITRARY CHARACTER SETS
by John McCarthy
It would be nice to be able to have documents stored in computers that
could include arbitrary characters and to be able to display them on
any CRT screen, edit them using any keyboard, and print them on any
printer. The object of this memorandum is to suggest how to get there
from here with special reference to the ARPA network.
Where are we now?
(1) At present, there is 96 character ASCII, and everyone agrees that
it should be included in any larger set.
(2) Many installations are dependent on 64 character sets which do not
even include the lower case latin alphabet.
(3) At the Stanford Artificial Intelligence Laboratory, we have a 114
character set that includes 96 character ASCII and which is
implemented in our keyboards, displays, and line printer
(4) Printers are becoming available that get their character designs
out of memory, for example, the Xerox XGP printer, one of which we are
(5) The IMLAC type display has the character designs in main memory so
that changing the displayed set is just a matter of reloading the
(6) Many display systems share the character generator among many
display units. In some of these, e.g. the Datadisc, arbitrary sets
are probably feasible (using kludgery to be described later), but in
other systems, e.g. our III's arbitrary sets are not feasible.
One possible approach to communication in expanded character sets is
to produce an expanded standard set of characters, perhaps using 8 or
9 bits and expect new equipment to implement this set. This approach
has the disadvantage that it will be very hard to get agreement on
what the next step should be, and even if formal agreement is
realized, many groups will find it in their interest to ignore the
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ARBITRARY CHARACTER SETS by John McCarthy
Therefore, I would like to suggest that the next step be to arbitrary
character sets. I suggest implementing this in the following way:
(1) There be established a registry of characters. Anyone can
register a new character. Each character has a unique number, 17 bits
should be enough even to include Chinese. Besides this, each
character has a name in ASCII usually mnemonic. Finally, the
character has a design which is a picture on a 50 by 50 dot matrix.
(2) Besides the registry of characters, there is a registry of
characters sets, which different groups are using for different
classes of documents. A registered character set has a registry
number and a table giving the correspondence between the character
codes as bit sequences and the registered character numbers.
(3) Associated with a document is a statement of the character code
used therein. This may be one of the registered codes or it may
contain in addition modifications described by an auxiliary table
giving the code correspondence with registered character numbers. A
character code may have an escape character that says that the next
character is described by its registry number. The statement of the
character code may be a header on the document or the receiver may
have to learn it by some other means, e.g. because its library
catalog entry contains this information.
(4) Devices such as printers and displays draw characters in different
ways and standardization doesn't seem feasible at present. Therefore,
it is necessary to provide a way of going from the standard
description of a character using a 50 by 50 dot matrix to whatever
method the device uses. This is up to the programmers who are
supporting the device. Some may choose to manually create files
describing how registered characters are implemented. They may find
it too much work to provide for all the characters and to update their
files when new characters are registered. Others will provide
programs for going from the registered descriptions to descriptions
compatible with their implementations. Perhaps most will hand tailor
the characters most used and provide a program for the others.
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ARBITRARY CHARACTER SETS by John McCarthy
(5) The easiest device to handle is the line printer because it is
slow. At the beginning of the print job, the SPOOL program will look
up the character set and load the printer's memory with the character
designs used in the particular document. Sometimes, it may have to go