Three machines, three paradigms, twenty years.

The 1004 is not really a computer in any modern sense. It has no software, no instruction set, and no memory in which to hold either. And yet, through most of the 1960s, it computed payroll for the United States Army, processed inventory for Westinghouse, and printed insurance statements for Mutual of Omaha. To program the 1004 was to wire it.

A removable plugboard accepted patch cords that connected card-column readers to accumulator counters, comparison registers to selector flip-flops, and printer columns to whatever data source the operator had chosen to route there. A program of thirty-one steps was a particular pattern of cords. To run a different application, you removed the board and slotted in another, pre-wired one — a program library was a literal cabinet of plug-boards.

Programs were objects, not text. To swap one out, you used your hands.

The emulator preserves this conceptual model exactly. There is no source-code editor. Instead, a thirty-one-row table represents the plug-board: each row is one program step with selectors for source, operation, destination, condition, and what to do next (advance to the next step, jump, eject a card, print a line, halt). A live bezier-curve overlay draws the active wire on every machine cycle so you can watch the patch take effect.

Six worked sample plug-boards demonstrate the idioms a 1004 operator actually used: list cards, sum a numeric column, print a multi-field invoice, accumulate group totals, compute a payroll via repeated-add multiplication, and emit a header / detail / trailer report — all without leaving the thirty-one steps.

The 1005 is what happens when a unit-record machine grows up. UNIVAC kept the 1004's eighty-column card I/O, its drum printer, its six-bit BCD character set, and its familiar console — and then they replaced the plug-board with nine hundred and sixty-one characters of magnetic-core memory and a stored-program processor that understood twenty-one instructions.

For the first time on this product line, you could write programs in a real assembly language. SAAL — the Sperry-Rand Assembly Language — gave its users the familiar mnemonics: MOV for move, ADD and SUB, CMP for compare, BR for branch, BRC and BRZ for conditional branches. There were registers, there were labels, there were comments. After ten thousand wires patched into a thousand 1004 plug-boards, suddenly there was source code.

Storage was tight enough that programmers worked in characters rather than bytes. An entire production payroll might fit in 600 characters of core.

The emulator gives you the whole stack: a SAAL source editor with syntax highlighting, a working assembler that produces a memory listing, a character-addressable virtual machine, and a step debugger that walks the listing one instruction at a time. The same six-bit BCD encoding the 1004 used; the same card hopper, drum printer, and punched output stacker. You write your program in source, you assemble it, you run it on the cards in the hopper, and you read the output the printer drum produced.

Six verified samples ship with the emulator: HELLO writes a greeting; ECHO lists every card; ADDEM sums a numeric field; COUNT tallies the deck; SORTEM implements an in-memory bubble sort across cards; PAYROLL reads hours-and-rate cards and prints a gross-pay register. Each program fits in well under a hundred characters of source.

The Apollo Guidance Computer is the most famous computer ever built — it landed humans on the Moon. But what astronauts actually touched was the DSKY: a brushed-aluminum panel with twelve indicator lamps, a row of two-digit displays, three signed five-digit register fields, and a calculator-style keyboard of nineteen square keys. The DSKY did not require its operators to know anything about the AGC's instruction set — and most of them did not. It spoke a different language entirely.

That language was a Verb / Noun grammar. VERB 06 NOUN 17 ENTR meant display the spacecraft's current attitude. VERB 16 NOUN 36 ENTR meant continuously monitor the mission timer. VERB 37 ENTR 11 ENTR meant load major program eleven, the Earth-orbit insertion monitor. The astronaut's operator's manual was, in effect, a vocabulary of pairs.

VERB described the action. NOUN described the data. The astronaut's manual was a vocabulary of pairs.

This emulator reconstructs the Block II flight DSKY — the version flown from Apollo 7 onward. Authentic 530-nanometer electroluminescent green seven-segment digits, rendered in SVG with the appropriate glow. Period-correct lamp coloring (red TEMP and GIMBAL LOCK; amber PROG and RESTART; white for the rest). A faithful nineteen-key pad with the iconic action-key colors: gold for PRO, green for ENTR, red for RSET.

Eight major programs are implemented behaviorally, including the lunar-descent sequence P63 → P64 → P66. The headline feature is a scripted Apollo 11 descent demo that fires the legendary 1202 program alarm at the moment the real one did, on schedule, in the actual sequence. Press RSET to acknowledge it — just as Steve Bales did when he called “Go!” from Mission Control — and the descent continues to landing.