Re: HP & RPN


There was some RPN being used on calculators in the mid 60s. In late '65 or early '66, I used a big Friden (sp?) RPN desktop calculator that had a 4-register stack that was visible on the CRT display. (It was quite the thing at the time, at least in the physics department where I was working.) I would assume that there could have been other electronic calculators using RPN then, too.



I discovered in 1988 (!) that Soviets used RPN calcs
such Elektronika MK-52. I got 4 of this calculator and they
were really powerful at their time.
For further information, please visit:

AFAIK the Curta uses some kind of RPN, too.
Maybe all older mechanical calculating machines,
since this was the way to go for the 'CPU',
and the amount of temporary memory was always low those days;-)



I have a copy of the book "Algorithms for RPN Calculators" by John A. Ball, Wiley Interscience, 1978, ISBN 0-471-03070-8.

He starts with a history of RPN and I quote:

" In their advertisements and also in a letter to me, Hewlett-Packard Company (HP), the best known manufacturer of RPN calculators, says that RPN is based on a suggestion by Jan Lukasiewicz (1878-1956), and that RPN was invented and is patented by HP. Aside from the apparent contadiction in these two statements, I do not think that either of them is quite true. My first experience with RPN involved a nice old Friden EC-130 desktop electronic calculator, circa 1964. The EC-130 has RPN with a push-down stack of four registers, all visible simultaneously on a cathode ray tube display. Furthermore, they are shown upside down, that is, the last-in-first-out register is at the bottom. The same orientation is used in instruction books for HP calculators, perhaps by coincidence."

" Around 1966, the Monroe Epic calculator offered RPN with a stack of four, a printer, and either 14 or 42 step programmability. The instruction booklets with these two calculators make no mention of RPN or Jan Lukasiewicz."


" Hewlett-Packard Company is to be commended for the beautiful design of the original HP-35 calulator (c.1972). They avoided many of the pitfalls that lesser minds would have become mired in. HP provided many features in a truly concinnate way. But ignoring the foundations on which this accomplishment was built serves no purpose. In my view, the RPN calculator owes about as much to the venerable mechanical calculator, and to a number of anonymous designers, some of whom worked for Friden, as it does to Jan Lukasiewicz."

I hope you find this enlightening...


Gordon Dyer


"Algorithms for RPN Calculators" is the classic RPN reference work. If anyone is an RPN fan and doesn't have a copy, find one. You will cherish it.

Also, in the HP35 User's Manual, page i:

"The operational stack and reverse Polish (Lukasiewicz) notation used in the HP-35 are the most efficient way known to computer science for evaluating mathematical expressions"

From all the posts, it appears there is a 60's era history of non HP RPN machines. Perhaps some HP engineer decided to stick to his guns in favor of the more efficient RPN when the rest of the world went to equals signs and parentheses.

Is it just me? But I get the feeling that if that happened today, the engineer would get railroaded by marketing in a heartbeat.



I have followed the various RPN threads and I am wondering if the RPN fans are aware that a line of Burroughs (now Unisys) mainframes, starting with the B5000 (circa 1963) and continuing to the present, consists of true stack machines which perform all operations on the process stack using RPN.


HP always said that RPN is used on big irons too. So every time I used "my" HP-41 I had the feeling of using a somewhat advanced chunk of computer science. When I got familar with VM/CMS (IBM) I soon felt at home as the fundamental concepts are the same (on all computers I think).



Although algebraic expressions may be processed by simulating a stack on any computer, very few computers are true stack machines at the hardware level. Most computers are one- or two-address machines. The IBM 1130 was a one-address computer. The IBM 360 and its successors are two-address computers. Burroughs (Unisys) medium systems are three-address computers.

Stack machines are zero-address computers.

The number of addresses is specified with respect to the number of operand addresses included in a typical instruction.

A zero-address machine ADD instruction contains no operand addresses because the operands are implicitly the top two items in the stack.

A one-address machine ADD instruction contains one operand address because the other operand is implicitly the accumulator.

A two-operand machine ADD instruction contains the address of the first operand which is added to the second operand with the result being stored in one of the two operands.

A three-address ADD instruction contains the address of the first operand which is added to the second operand and stored in the third operand.

Burroughs stack mainframes use the stack for both data and control information. All operations, arithmetic, logical, and control, are performed using the stack.


The HP3000 minicomputers were also based on a true stack machine architecture, until PA-RISC came along and they emulated the classic 3000 processor in microcode. I believe that the first 3000 design dates back to around 1970 with the first hardware release in 1972. It would be interesting to know what (if any) connection there was between the calculators and the computer group at HP as far as the use of RPN. The 3000's had the top 4 stack entries in registers giving it much faster access to these items, something analogous to the direct access to the 4 stack registers on the 41C.

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