HP Calculators

The HP-65 was introduced in 1974, just 18 months after the introduction of the HP-35. The HP-65 packed a lot more functionality into a calculator that was about the same size as the HP-35. Most keys on the HP-65 had 4 functions, with the additional functions being accessed by the F (gold) and G (blue) "shift" keys or the "f-1" key. Among the added features were the ability to do base conversions between decimal, octal, and hexadecimal, and the ability to directly perform degrees.minutes seconds arithmetic (D.MS+ and D.MS-). The major improvement to the HP-65, though, was its programmability. The HP-65 had 100 lines of program space and used label addressing. It was billed by HP as "The Personal Computer". Programs were stored on magnetic strips. Users could write their own programs or purchase them from HP. One interesting fact about the HP-65 is that it was used by US astronauts to calculate course corrections when rendezvousing with the Soviet Soyuz spacecraft in 1975.

The HP-41 calculator was introduced in 1979 as a Personal Computing System. The display and keyboard were greatly improved over HP calculators, and the HP-41 really was much more than "just" a calculator. The display was a multi-segment LCD that allowed display of true alphanumeric data, and the keyboard allowed full alphanumeric data entry. Besides that, the keyboard could be placed into "User Mode" which allowed the user to assign any function - either built in or programmed - to any key. HP also sold blank keyboard overlays so that users could customize the labeling to match the programming. Program memory was non-volatile, and pre-written software (application packs) came on ROM modules. The HP-41 didn't come with a built in card reader, but an add-on card reader could be purchased for users who wanted to save their custom written program to magnetic strips. The HP-41 series is probably the most powerful non-graphing calculator ever produced, and there is much more information available than will fit into a few paragraphs. An HP-41 simulator that runs on Windows is available here.

The HP-11C was the first calculator in Hewlett-Packard's 10C series. Built in functions included hyperbolic and inverse hyperbolic trig functions, probability (combinations and permutations), factorial, % change, absolute value, and a random number generator. The HP-11C also had a limited "User" functionality that allowed the labeled (A - F) gold keys to be assigned user written programs. Compared to other calculators in the 10C series, the HP-11C had advanced programming capabilities. The HP-11C had 63 lines of permanent program space, 20 general purpose registers, and 1 dedicated Indirection (I) register. As programs grew larger than 63 lines, registers were automatically converted into additional program. Each register converted into 7 lines of program space, so if all 20 registers were converted to programming space a program could be up to 203. Programming constructs provided by the HP-11C included labeled addressing (0-9 and A-E), subroutines (nestable to 4 deep). 8 conditional tests, increment/decrement loops, and 2 flags. Indirection (via the I Register) was allowed on STO, RCL, GTO, and GSB instructions, the display modes, and exchange (exchange X with the register indicated by i). The I register could also be used with the ISG (Increment then Skip if Greater) and DSE (Decrement then Skip if less than or Equal).

The HP-15C calculator was designed for math majors and others who needed to do complex mathematical calculations. It had built in support for complex numbers (numbers that include both a real and an imaginary part) and matrix math. Built in matrix operations included basic functions as well as more advanced matrix functions such as determinants, inverse, and LU decomposition. Like the HP-11C, up to 5 keys on the HP-15C could be assigned to user written programs.

In my opinion, the HP-16C was the most interesting calculator ever produced by any company. Designed for computer scientists at a time when programmers were concerned with bits and bytes, the HP-16C could display numbers in binary, decimal, octal, and hexadecimal. Besides just being able to display numbers in various formats useful to computer programmers of the time, the HP-16C could be set to act like just about any microprocessor. Word length could be set to any length from 1 to 64 bits. Math could be performed as unsigned, 1's compliment, or 2's compliment. Overflow and carry flags worked just as they would on an actual microprocessor. The HP-16C even offered 2 different ways to do floating point math, HP-16C native and IEEE standard. Other functions that made the HP-16C useful to programmers included shift, rotate, bitwise functions (AND, OR, NOT, and XOR), bit setting and testing, flag setting and testing, and many others. Truly a unique calculator.