Bally Professional Arcade / Astrocade

The display at 160×102 with 2 bits per pixel consumed 4,080 bytes — virtually all of the machine's 4 KB of RAM. To fit a BASIC interpreter at all, Fenton interleaved every bit of the program with the display: BASIC used the even-numbered bits, the display used the odd-numbered bits, and the interpreter read two bytes, dropped every odd bit, and reassembled one byte of code. The program was hidden in plain sight by setting two of the color register values to the same white, so the presence or absence of a program bit had no visible effect. Scavenging a few display lines (88 instead of 102) yielded 1,760 bytes for BASIC programs. The screen you watched was also the memory your program occupied — an extreme version of "the program lives in the display."

Programs were entered on the 24-key hex keypad with a plastic overlay mapping letters, symbols, and BASIC keywords, selected through four colored shift keys: typing WORD (gold shift) then "+" produced GOTO. A simple line editor was supported — after typing a line number, each press of the PAUSE key loaded the next character from memory. The machine was designed to be programmed the way you'd use a calculator, on a TV, in a living room. The keypad layout and bit-interleaved memory are the museum's strangest programming ritual outside the TI-59's magnetic cards.

The controller is a pistol grip with a trigger switch on the front, a small 4-switch/8-way joystick on top, and a shaft connected to a potentiometer so the stick rotates to double as a paddle controller. This hybrid — trigger, joystick, and rotating paddle in one hand — is the same "one grip, several grammars" idea as the Fairchild Channel F's twist-grip (both from 1976–78), but executed with a trigger plus a rotary joystick rather than a twist cap. Bally BASIC even exposes the inputs as functions: JX()/JY() for the joystick, KN() for the knob, TR() for the trigger.

The museum's RCA Studio II (1977) has keypads on the console; the Coleco Telstar Arcade (1977) is a triangular body-as-controller; the Fairchild Channel F (1976) has a twist-grip. Bally adds a programmable console whose code is physically interleaved with its own display — no other exhibit makes the program memory and the picture the same RAM. The ZGRASS expansion (with its full keyboard and GRASS language, later released as the Datamax UV-1) completes the story of a console that tried to become a computer.