HP 9815A calculator The desktop calculator HP 9815A was introduced in 1975 as the first of the third-generation desktop calculators. It uses a 16-digit plasma display (gas-discharge display) made by Panaplex and a commercial microprocessor, a Motorola type MC6800 with internal paralel bus. The calculator has a thermal printer and a tape cartridge for data storage. In contrary on its predecessors first generation desktop calculator (HP 9100A/B) and second generation (HP 9810A and HP 9820A), the HP 9815A stores programs and data on magnetic tape cartridge known as DC100 or HP200. Each DC-100 mini-cartridge has capacity of 94K bytes and was much smaller, lighter, and cheaper than the first- and second-generation of HP desktop calculators. For programming, the HP 9815A uses RPN (Reverse Polish Notation) system used on the handheld calculators with a four level stack with all results in the x register. The calculator has 472 program steps optionally expandable to 2008 steps. Price in year 1975 was US$2900.