Missing Math

The Hewlett-Packard 71B is arguably one of the most potent pocket computers ever produced. However great this system was, it suffered several limitations, some by design! HP used one of these limitations by design as a selling point: buy the platform, and expand it as needed so that it could fit your computational needs. And indeed, this was true. One could easily spend the double of the base cost – already hefty –, in extensions. Fair enough, not everyone needed a FORTH/Assembler module.

But HP made a huge mistake according to many users: cram into the limited ROM space of the 71B a useless algebraic CALC mode – I would even call this a heresy – while relegating critical mathematical capabilities to a costly expansion module. The 32KB HP-82480A MATH module (5061-7226) cost ~$100 in 1985. Count several times this value today!! Think about this module as the equivalent of an HP-15C, one of the best scientific calculator of the time. I attached for your reference an article form the July 1984 edition of the Hewlett-Packard Journal.

The most infuriating fact about this original omission is that the MATH ROM is an engineering feat, which happened to exhibit no bug what so ever. And this is remarkable as all its routines are compliant with the then proposed IEEE floating point math standard! Impressive. All the more so, the computations on the added new COMPLEX data type, and ARRAYs, are handling infinity and NaN seamlessly. From a software engineering point of view, this is also amazing as HP engineers implemented the new data type in two precisions, using pointers to reference the real and imaginary parts in variables/registers’ encoding. An excellent hack of the existing codebase. So, if you ever plan to pick-up an HP-71B and can afford a single expansion module, make it the HP-82480A one.