HP RPN

Implementations of Reverse Polish Notation by Hewlett-Packard

First version

• HP 9100
  • Three-level stack; registers X, Y, Z
    • X: ‘keyboard register’ - this is where input is stored
    • Y: ‘accumulator’ - results of arithmetic on X and Y stored in Y
    • Z: ‘temporary’ register - called ‘T’ in later four-level stack implementations
  • Entire stack displayed simultaneously on a 3.25" x 4.75" green CRT (but orange register labels for 9100B)

Stack manipulation keys

↑

(enter)

↓

(drop)

ROLL ↑

ROLL ↓

x⇄y

(X and Y exchange)

Storage registers

• HP-9100A
  • 16 (0-9, a-f) and 196 program steps
    • pressing a-f keys auto-recalled register value
• HP-9100B
  • 32 (0-9, a-f on each of two pages labelled ‘+’ and ‘-‘) and 392 program steps

References

• https://www.hpmuseum.org/hp9100.htm
• https://www.hpmuseum.org/rpnvers.htm