The Museum of HP Calculators


HP-21 Features

Features in optional ROMs are listed as Option.
Features in HP mag card or tape Application Pacs are listed as +.
Other software is not included.

Display and Keyboard HP-21
Display type LED
Display format 1 Line
FIXed number format Yes
SCIentific number format Yes
ENGineering number format -
STanDard / ALL number format -
Alpha messages and prompts -
Softkeys labeled by mag. card or overlay -
Softkeys labeled by display menus -
Softkeys with neither labeling system -
Status annunciators -
Redefinable keyboard -
   
Logic HP-21
Logic system RPN
Stack levels 4
Last x -
Undo -
Precedence -
Parentheses -
Storage Addition (STO +) -
Storage Arithmetic (STO +, -, ×, ÷) Yes
Storage Exponentiation (STO ^) -
Recall Arithmetic -
Named variables -
Multiple data types -
Directories -
   
Math HP-21
+, -, ×, ÷ Yes 
1/x Yes
sq. root Yes
x2 -
LOG x Yes
10x Yes
LN x Yes
ex Yes
yx Yes
pi Yes
% -
% change -
INTeger truncation and ABSolute value -
Trigonometric functions (SIN, COS etc.) Yes
Hyperbolic trig. (SINH, COSH etc.) -
# of trig. modes (degrees, radians, grads) 2
   
Advanced Math HP-21
Solver / root finder -
Numeric integration -
Complex numbers -
Matrix operations -
Matrix writer -
Equation writer -
Symbolic operations -
Fractions -
Plotting and graphics (display) -
Plotting and graphics (printer / plotter) -
   
Statistical HP-21
Mean, standard deviation (# of variables) -
Summation of n, x, x2 -
Summation of n, x, x2, y -
Summation of n, x, x2, y, xy -
Summation of n, x, x2, y, y2, xy -
Summation of lists -
Random number generator -
Linear regression, estimate  -
Curve fitting -
Correlation coefficient -
Normal distribution -
Factorial -
Gamma -
Combinations and permutations -
   
Scientific and Time

HP-21

Polar / rectangular conversions Yes
Base conversions (2, 8, 10, 16) -
Arithmetic in bases 2, 8 and 16 -
Bit operations (AND, OR, XOR, ...) -
Selectable word size (1-64 bits) -
Selectable complement mode (1's, 2's, unsigned) -
Decimal hrs / hrs.min.sec. conversions -
Hrs.min.sec arithmetic -
Time of day clock -
Timer -
Dynamic calculations (timer × rate) -
Alarms -
   
Unit Conversions

HP-21

Centimeters / inches -
Millimeters / inches -
Meters / feet -
Kilograms / pounds (mass) -
Newtons / pounds (force) -
British thermal units / joules -
Liters / gallons -
° Celsius / ° Fahrenheit -
Other -
User-defined units -
   
Time Value of Money HP-21
Number of payments (n) -
Interest rate (i) -
Present Value (PV) -
Payment (PMT) -
Future Value (FV) -
   
Cash Flow Analysis HP-21
Net present value (NPV) -
Internal rate of return (IRR) -
   
Amortization HP-21
Accumulated Interest (ACC INT) -
Balance (BAL) -
   
Depreciation HP-21
Straight line (SL) -
Sum of the years digits (SOYD) -
Declining balance (DB) -
   
Bonds and calendar functions HP-21
Bond price -
Bond yield -
Date arithmetic / calendar functions -
   
Memory and Programming HP-21
Programming language(s) -
RAM / Max # of variables or addressable registers 1 Register
Max # of program steps -
RAM / Max vars or regs with full optional RAM -
Max # of prog steps with full optional RAM -
Merged program steps 

-

Manual register / program memory allocation  -
Automatic register / program memory allocation

-

Overlapped register and program memory -
Continuous memory

-

Flags -
Conditional tests -
Subroutine levels -
Indexed looping (increment by +/- 1, end at 0) -
Indexed looping (choice of increment and end) -
Multiple index / loop registers -
Line number addressing -
Branching by relative line number -
Global program label addressing -
Local program label addressing -
Indirect / computed addressing and control -
Multiple indirection registers -
Pause -
Alpha messages and prompts in programs -
Alpha program listings -
Alpha string manipulation -
Program step insert / delete -
   
I/O and Expansion Features HP-21
ROM modules -
RAM modules or expansion option -
General expansion slots / connector -
Magnetic card reader/writer -
Tape drive -
Disk drive -
Upgradeable firmware -
Optical wand -
Serial port -
Infrared input -
Infrared output -
Printer -
Networking -
Other -
   
General HP-21
Sounds -
Self test -
Hard case (in addition to soft case) -
Additional Features -
Batteries Rechargeable
Length (inches) 5.1"
Width 2.7"
Height 1.2"
Weight (oz or lbs) 6 oz
Year of introduction 1975

Features in optional ROMs are listed as Option.
Features in HP mag card or tape Application Pacs are listed as +.
Other software is not included.

Unlim means limited only by available memory.

HP-21 notes:
  • FIXed display selected by DSP . #. SCIentific display selected by DSP #.
  • The HP-21 had dedicated keys for storage arithmetic: M+, M-, M×, and M÷

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