history of the 4-level stack

[Jeff_Kearns]

(09-05-2014 09:11 PM)axd1967 Wrote:  Hello,

I'm trying to find out what lead HP to evolve to a 4-stack layout.

Here is a copy/paste from HP Solve Issue 14, 2009-08: The “RPN” Stack - Future & Past (Part 2)

Quote:The “RPN” Stack - Future & Past (Part 2)

In the last issue of HP Solve the RPN stack was described and a resource was referenced that provided all possible reorganizations of the four stack registers. The article finished with the following paragraph. “Why is the HP RPN stack four high? Why did HP use RPN? What was the basis for the first HP RPN pocket calculator? These and other RPN related questions will be discussed in our next issue.”

On May 14, 2009, there was a special event at HP Labs when an IEEE (Institute of Electrical and Electronics Engineers) milestone in electrical engineering and computing presented a plaque honoring HP for its work on the first pocket scientific RPN calculator, the HP-35A. HP invited all members of the HP- 35A design team to attend the award ceremony, and it was a great opportunity for HP Solve to talk to Tom Osborne, the engineer responsible for bringing RPN to HP in the mid 60’s.

Tom designed and built the prototype machine that formed the basis for the HP9100. This famous machine is called the Green Machine because of the Cadillac Green Metallic paint he used on its balsa wood case.

When the HP 9100 was finished Bill Hewlett asked if the same capability could be put into a shirt pocket and the HP-35A evolved. See figure 1. One of the unique features of the HP 9100 was that it included transcenddental functions.

According to Tom the HP-35A stack was only four registers high because that is all that the memory budget would allow. Memory technology was in its infancy and still very expensive. The HP 9100 stack was only three registers high. Tom wanted to make the stack as high as possible. Tom Osborne had spent time at SCM working on an electronic calculator and he had been exposed to RPN. RPN is a natural way to implement arithmetic in electronic circuits. Here is how Tom Osborne explains it.

“No one that I knew at HP Labs was familiar with RPN when I designed the 9100A. The green machine I took to HP was an interesting combination of infix for multiply and divide but post fix for add and subtract. The 9100A stack was high enough to solve most of the normal computations we encountered.
With a bit of mental parsing on the input a 2 deep stack can solve any two operand problem, so we were more than covered. A really deep stack is required if one goes formal and leaves all of the operands in their original order and then relocates the postfix operators (as a full blown parser does).”

“The 9100A stack left the results of a computation in the next to the bottom of the stack (the Y register) - a normal RPN machine would drop the result of a calculation into the bottom of the stack - as I recall, that is what Friden did, and I wanted to avoid any patents they may have had.”
“I also inverted the stack's direction from what was done in computers. That way the dividend and divisor were properly located with the divisor below the dividend. Bob Barton went the other way because he visualized the stack as a stack of dishes at the front end of a cafeteria line where one takes the dish at the top of the stack rather than the one at the bottom of the stack.”

“I probably would have used postfix on store if we had more than 10 storage cells (0-9), but "STO N" seemed much more easily understood than "N STO". However with more than 10 numeric memory cells then RPN would have won because it saves a keystroke. "STO 11" would have to be "STO 11 Enter" vs. "11 STO".”

“By the way, I don't remember how PFN (for Parenthesis Free Notation) first came up. It may have been a customer recommendation. I wish I had thought of it at the beginning - but it’s never too late to make things right ... right?”
You may read more about the development of the HP9100 by Tom Osborne at:
http://www.hp9825.com/html/osborne_s_story.html

[/code]