TI-59

The TI-59's magnetic cards were a triple-use medium. Sliding a card through the side reader loaded or saved a program (the machine's motor pulled the card through; one quarter of memory was stored on each side). The card's top surface was left writable, so the programmer could hand-write the program name and notes. And once read, the card slipped into a slot between the display and the keyboard, where its printed side became the live legend for the five user-defined label keys A–E and their shifted A'–E' forms. Storage, manual, and interface label were the same physical strip of plastic — a compact, tactile answer to the problem of software documentation.

Programming the TI-59 meant simply switching to learn mode and pressing keys: the calculator recorded the keystroke sequence as the program, merging up to eleven keypresses into single instruction steps. It supported labels, conditional branches, loops (increment/decrement and skip on zero), indirect addressing, user flags, subroutines, and alphanumeric output through the PC-100 printer cradle. Because the language was Turing-complete, hobbyists wrote games — BYTE published "Darth Vader's Force Battle," a type-in program for the TI-58/59, in October 1980 — and professionals used it for everything from real-estate calculations to aviation. The TI-58 (no card reader, half the memory) was even used aboard the Hawker Harrier for stabilization during takeoff and landing.

TI packaged expertise as physical modules: the Solid State Software ROM cartridges, which plugged into a compartment on the calculator's back, ran directly from ROM so they did not consume the user's program memory. The Master Library (25 programs) was included; modules for statistics, real estate, investment, surveying, and aviation were sold separately, each shipping with plastic overlay cards that labeled the user-defined keys. From November 1977, TI also ran the PPX-59 (Professional Program Exchange): users submitted programs and bought back packs of magnetic cards by mail — software distribution as a physical, postal system, a decade and a half before the internet app store.

The TI-59 sat at the hinge where the calculator stopped being a calculating machine and became a pocket computer: Turing-complete, externally storable, expandable, with a printer, a program exchange, and a large community. It was available from 1977 through 1983, and institutions kept it longer — the Science Museum Group holds books of TI-59 program cards in its collection, and The Henry Ford holds a TI-59. It is the ancestor of every pocket computer and laptop that followed, and the last mass-market device where your program lived on a strip of plastic you could hold in your hand.