HP-65

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The HP-65 is the first handheld programmable calculator, and it included a magnetic card read/write system for program storage. Introduced by Hewlett-Packard in 1974 at an MSRP of $795 (equivalent to $5,190 in 2025), it featured nine storage registers and room for 100 keystroke instructions. It also included a magnetic card reader/writer to save and load programs. Like all Hewlett-Packard calculators of the era and most since, the HP-65 used reverse Polish notation (RPN) and a four-level automatic operand stack. Bill Hewlett's design requirement was that the calculator should fit in his shirt pocket. That is one reason for the tapered depth of the calculator. The magnetic program cards are fed in at the thick end of the calculator under the LED display. The documentation for the programs in the calculator is extensive, including algorithms for hundreds of applications, including the solutions of differential equations, stock price estimation, statistics, and so forth.