ADM-3A

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ADM-3A
Developer:	Lear-Siegler

The ADM-3A is one of the first computer terminals manufactured by Lear-Siegler. It had a 12 inch screen displaying 12 or 24 lines of 80 characters, and one of the most rugged chassis ever to be employed in any computing equipment, being constructed with a very thick metal frame (over an inch at the thickest bits). The downside of this ruggedness (including a wire mesh covering ventilation and cooling apertures, making the computer a Faraday cage) was that it weighed in at a whopping 32 lb (approx. 14.5 kg). The streamlined look of the terminal was decades later emulated by the iMac computer-line of Apple Computer.

Originally priced at $1195, a DIY kit later sold for $995. At first only allowing capital letters as ADM-3; the model was quickly supllanted 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 daisychaining of 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.

The 5x7 dot matrix characters were displayed in amber, green phosporous or white on black (the cursor was 7x9). The keyboard had 59 keys, including a "here is" -key which would identify the terminal to the computer it was connected to.