The ADM-3A was one of the first computer terminals manufactured by Lear Siegler. It had a 12 inch screen displaying 12 or 24 lines of 80 characters.

Details

ADM3A keyboard layout

Originally priced at $1195, a DIY kit later sold for $995. At first only allowing capital letters as ADM-3; the model was quickly supplanted by the more advanced version with both lower case, and uppercase. Further optional Add-ons included a graphics card enabling it to emulate a Tektronix 4014 and an extension port which would allow daisy chaining several ADM-3As on a single RS-232 line. The setup was controlled by 32 DIP switches under the nameplate at the front of the machine, beside the keyboard, including speed from 75 to 19200 bit/s (although all speeds above 9600 were purely theoretical, as it could accommodate such speeds only if the actual incoming characters were coming at a much slower rate to accommodate its buffer, otherwise data would be lost). The advanced configuration options allowed split speed connection, sending at one rate, and receiving at another.

Hardware

The 5x7 dot matrix characters were displayed in amber, green phosphorus or white on black (the cursor was 7x9). The keyboard had 59 keys.

Legacy

The practice of using the Tilde character for the "Home" directory on Unix and Unix-derived systems derives from the fact that the ADM-3A happened to have the Tilde symbol and the word "Home" on the same key. The use of the HJKL keys for moving the cursor in the vi editor and its descendants also stems from the ADM-3A - it had the cursor-movement arrows printed on those four keys.

External links

• Lear Siegler ADM 3A
• Tenth Anniversary ADM 3A Dumb Terminal Video Display Terminal User's Reference Manual

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