1968 · Programmable Desktop Calculator · Work 931 of 1,871
A physics laboratory at a university in California, on a black laboratory bench a broad desk calculator forty centimetres wide in pale grey-white metal, slightly wedge-shaped, at the top a wide dark-tinted screen with a soft even green glow, below it a row of small toggle switches and a card slot at the right, on a dark grey tray four blocks of square keys in grey, cream and dark grey, every key plain smooth and unmarked, a hand in a white shirt cuff sliding a plain grey magnetic card into the slot, a green oscilloscope beside it, through the open doorway a bare corridor ending at a closed grey steel door, morning light.
What it was used for
HP's first calculator, a programmable desktop machine of about 18 kg at 4,900 dollars. The green 3.25 × 4.75 inch CRT showed the whole stack: 3 registers X, Y and Z in reverse Polish notation, 10 visible mantissa digits and 2 hidden guard digits. Program and data shared the core memory, at most 196 steps and 16 registers, 1 register being equivalent to 14 program steps. Programs were stored on a magnetic card shaped like a credit card but somewhat smaller, 2 tracks of 196 steps each, with a clipped corner to block overwriting. The case was cast aluminium. The 9100A later fell to 4,400 dollars; its successor 9100B started again at 4,900 dollars.
What was new
Programmable desktop calculators with magnetic cards were not new; the Olivetti Programma 101 came before. What marked the 9100A was that it computed trigonometric, logarithmic and exponential functions at a keystroke, displayed the stack on a CRT, and needed not a single digital integrated circuit to do it: its fixed program lay as printed conductors on circuit boards. Because program and data shared one memory, a program could modify itself, and a running program could be resumed after the machine was switched off. Bill Hewlett later demanded that same power in a shirt pocket: 4 years on, the HP-35 did the same transcendental functions.
What the sources leave open: The Museum of HP Calculators supports prices, memory sizes and construction. Why HP called the machine a calculator is not stated there. The Hewlett-Packard Journal of September 1968 was available only as page images and could not be read, so computing speed is left unsupported here.
Connections
Every connection names its kind. “Forerunner” on its own would be a claim.