history of the 4-level stack

[Jeff_Kearns]

(09-05-2014 09:11 PM)axd1967 Wrote:  [1] http://www.hpmuseum.org/rpnvers.htm#3level
[2] HP-67 Owners Handbook, p. 66 (Automatic stack)
[3] HP-41 C/CV Owner's hb, Section 3 (Automatic stakc)
[4] HP-41 CX owners manual vol 2, p177
[5] https://delicious.com/axd/HP,stack

Hi Alex,

Your main questions seem to be, why did HP evolve from a 3-level stack in the 9100 (circa 1968) to a 4-level stack in the HP-35 (circa 1972), and why are there not less or more than 4-level stacks in classic RPN?

First off, the 'true' history of RPN seems rather muddled, and I suggest you read the evolution of RPN and numeric entry on the museum site as a starting point.

The highly recommended reference book: "Algorithms for RPN Calculators", by John A. Ball, 1978, has a section on the history of RPN, wherein he claims the RPN calculator "owes about as much to the venerable mechanical calculator, and to a number of anonymous designers, some of whom worked at Friden, as it does to Jan Lukasiewicz".

'The Definitive Guide to How Computers Do Math", by Clive Maxfield and Alvin Brown, 2005, states that Charles Leonard Hamlin (1822-1985), one of Australia's first computer programmers, pioneered the placement of operators after the operands, and that his method is what became known as reverse Polish notation (RPN).

Even though the Friden EC-130, circa 1964, and the Monroe Epic Calculator, circa 1966, do not mention "RPN" or Lukasiewicz (roughly pronounced woo-ka-shea-vich), they clearly operated according to a postfix, parentheses-free, 'RPN'-like fashion - and they each had a 4-level push-down stack. Undoubtedly, HP improved on this with the repeating T register and seems to be the first company to use the term RPN (which they patented).

I think if you search the archives you will many discussions about RPN stack levels and I would say Jose Mesquita provided a good summary in his response - that it is all about compromise. Less than 4 levels is undesirable (a 2 level stack would be the absolute minimum to even qualify as a calculator) and more than 4 level stacks would make memorization of stack contents difficult for most people.

Jeff K