HP 9820A  Introduction
The desktop calculator HP 9820A, introduced in 1972, was the first HP calculator with algebraic entry system.
However, the HP9820A uses algebraic entry system
only at user lever. Internally, the calculator use RPN (Reverse Polish Notation) system. All entries are translated into RPN.
The HP9820A has very similar hardware structure
like predecessor HP9810A.
The threeline LED display at HP9810A
was replaced by oneline 16character 5x7 dotmatrix LED display.
The calculator HP9820A without options has five functions (add, subtract, multiply, divide, and square root) and six memory
registers (named A, B, C, X, Y and Z). The calculator has
a 16column thermal dotmatrix printer and a 2"wide magnetic card reader. The magnetic card reader is improved and in the
contrary to HP9810A and
HP9100B
accepts magnetic cards in both directions. The standard magnetic card which is six inches long can store max. of 45 memory
registers on each direction. An expanded magnetic card long 10½" has space for 90 memory registers on each direction.
Like the predecessor HP9810A the calculator HP9820A has 4 slots in the rear for interface boards. To the interface board exists an I/O expander for next 9 slots.
Price for HP9820A without ROMs was in year 1972 around US$5000.
