Most of the computer terminals at the Stanford AI Lab are display
terminals; a few are vector-oriented, built by Information International,
Inc. (hereafter called IIIs) and the rest use standard TV monitors built
by Ball Miratel (hereafter called Data Discs because the controller for
them was built by Data Disc).  These terminals use keyboards which
generate an extended version of the usual ASCII character set.  The normal
7-bit ASCII codes are all used for graphic characters, and control
functions are provided by two extra bits generated by the CONTROL and META
keys.  Thus, while the CONTROL key on a standard ASCII terminal subtracts
100 (octal) from the character code, our CONTROL key adds 200 and our META
key adds 400.  Also, two special keys, ESC (escape) and BREAK, generate
special codes which are not transmitted to user programs at all, but are
directly interpreted by the timesharing monitor as special commands
affecting the terminal.  These commands are explained at length in Section
2 of the Monitor Command Manual, SAILON 54.3, which is available online in
the file MONCOM.BH[S,DOC].  If you are logged in at a display terminal,
you can print a concise list of ESC and BREAK functions, and a table of
the extended ASCII character codes, on the Xerox Graphics Printer by
typing HELP DDKEY if you are using a Data Disc or HELP IIIKEY if you are
using a III.  The list is designed to fit in the indentation provided for
the purpose at the top of the keyboard.

A new display type is the Datamedia 2500A with "SUMEX" keyboard, or any
other display which emulates one (e.g., Imlacs, Datamedia 3025).
Datamedias (DMs) are lower-class Datadiscs:  they are slower and don't
provide graphics capabilities.  However, they may be used remotely from
the AI Lab over dialup telephone lines.  For more information about DMs,
say HELP DM.  To get a crib sheet of display commands for DMs, say HELP
DMKEY.  If you want to use a DM to access the ARPAnet via the SU-TIP, say
HELP SU-TIP.