Chuck Moore on stack size, stack operators and function arguments

[Steve Simpkin]

(11-09-2024 07:08 PM)knife31 Wrote:  ...
That being said how did HP decide that RPN was the way to go, did they use Forth or RPN exclusively for basic and advanced math and were there holdouts.
RH

To better understand RPN logic and why HP used it, you need to look at some of the history of electronic scientific calculators.

HP models, with their RPN logic and a four level stack, were able to provide a workable entry system that allowed most problems, even complex ones, to be solved without writing down intermittent results. The major advantage of using this logic system is that it greatly reduced the system complexity and RAM/ROM requirements over trying to implement an algebraic entry system that supported parenthesis and rules of operation precedence. The RPN methods used to break down a problem and to work it from the inside out also had the added advantage of mimicking the methods you would have used to solve the problem with a pencil and paper (or a slide rule). This made it easier to learn by someone who was already used to solving those type of complex problems in this manner.

Conversely, the early TI models without parenthesis keys (for example the SR-50 and SR-51) were not easy to use on complex calculations. The mental gyrations needed for calculating parenthesis heavy formulas could be daunting if you didn't break down the equation into simpler subsets first. Even then, this may have required intermediate results to be written down and re-entered in order to solve some problems. The fact that TI didn’t introduce a model with Algebraic Operating System (AOS) and parenthesis until September 1975 (the SR-52), a full 3-2/3 years after the HP-35, really drives home how difficult it was to implement at the time. Even these early TI models still used RPN entry for single argument functions like Sin and square root. It was not until around 1990 when TI introduced its EOS logic on the TI-81 that they had what could be considered a true algebraic entry system, 16 years after the introduction of the SR-50.

The following Datamath page describes the long evolution that TI had with algebraic entry on their calculator models.
http://www.datamath.org/Sci/WEDGE/SR-52_...ing_System: