ADM -3A is an ASCII computer terminal, built by Lear Siegler and from 1976 on the market, one of the first computer terminals. It could represent on his 30 cm (12 inches) monochrome screen calibrate 12 or 24 lines of 80 ASCII characters. It has an advanced typewriter keyboard with 59 keys, QWERTY occupancy, with some specially assigned keys. Via a serial interface, selectable according to the standard EIA- 232 or 20 mA Telegraph port it is connected to the host computer. It was a kit for the price of $ 995, - or as ready- assembled unit to U.S. $ 1195, - available.

The original version, the ADM -3, could only represent uppercase. The configuration was about 32 DIP switches, among other things could the data transfer rate 75-19200 bps can be set. As a special feature, and in contrast to later-developed computer terminals such as the VT100, the ADM -3A does not use a microprocessor. The entire circuit consists of a plurality of logic blocks 74xx with which also the complete video controller and the cursor control are realized. The only higher integrated circuits are the Universal Asynchronous Receiver Transmitter ( UART), the RAM memory than text memory and a fixed programmed ROM chip that contains the character set.

In an ADM -3A of early vi text editor was written in 1976 by Bill Joy. Since the ADM -3A for cursor control, H, J, K and L keys used, also on the corresponding commands in vi derived.