9821A Advertisement
Electronics Magazine, January, 1974

The Hewlett Packard 9821A is a follow-on to HP's 9820A calculator, introduced in December of 1973. Primarily, the 9821A replaces the 9820A's magnetic card reader/writer used for storing programs and data, with the digital compact cassette tape transport used in the HP 9830A BASIC-programmable calculator.

The cassette tape drive provides significantly more flexibility over the magnetic card device. The capacity of the cassette tape is much higher than the magnetic card. The magnetic tape drive can be used for data storage in a program without operator intervention, as well as for loading and execution of programs from the tape, allowing for programs of almost unlimited size.

The 9821A added additional functions to its programming language to allow programmed control over the tape drive. The machine provides a base of 167 memory registers, versus 173 in the 9820A, due to additional RAM being used by the firmware for managing the cassette tape drive. The 9821A provides considerably more memory expansion capability than the 9820A, with up to 1,447 memory registers versus the 492 register maximum of the 9820A. The combination of these benefits make the 9821A capable of much more complex applications than could be implemented on the 9820A.

The 9821A is identical to the 9820A in many of its components, including the power supply, keyboard, display, printer, and HP mini-computer derived four-board bipolar serial CPU. RAM and ROM boards are similar, as well as the I/O interface circuitry for the keyboard, display and printer. two machines. The main departure came with the replacement of the magnetic card reader/writer and its low-level interface circuitry with the digital cassette tape transport and its low-level interface circuitry borrowed from the 9830A. The embedded ROM firmware for the 9821A was a reworked version of the 9820A firmware, which includes efficiency updates as well as replacement of the magnetic card device driver code, with ability to control the cassette drive, as well as modification to allow the calculator to address more RAM.

The Old Calculator Museum is looking for a good condition (but not necessarily working) 9821A to include in the collection. If you have one that needs a new home in a museum, please get in touch by clicking the EMail button in the menu bar at the top of this page.