HP9100 Prototype Desktop Electronic Calculator

This transistorized electronic calculator is the prototype for the first electronic calculator sold by Hewlett-Packard Company, the HP 9100. The machine was notable for its ability to compute transcendental functions at the push of a button, and for the range of values that could be computed.

The prototype has a metal case painted gray. At the right center is an array of nine digit keys and a 0 bar, with clear display, enter exponent, and change sign keys above these. To the right of these keys is an array of fourteen programming keys. Left of the digit keys are keys for arithmetic operations, square roots, and shifting the position of variables within the x, y, and z registers of the calculator . The fifteen further keys to the left are for a variety of trigonometric, hyperbolic, and exponential functions.

Above these keys are four switches. The leftmost determines whether angles entered and computed are in radians or degrees. The second switch from the left determines whether the decimal point is floating or fixed. The third switch turns the power on or off. The rightmost switch sets the mode as run or program. A display and a dial that may be set between 0 and 9 are behind the keyboard and switches. At the back are a power cord and a connector.

The prototype brought together ideas of Thomas Osborne, Malcolm McMillan, and others at Hewlett-Packard. For Osborne’s earlier prototype, see 19780311.01 and 1978.0311.02. For a production model of the HP9100B, see 2012.0044.01.

Bernard M. Oliver, “How the Model 9100A Was Developed,” Hewlett-Packard Journal, September, 1968. A copy of this article is at the HP Museum website.

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