Abstract: An adaptable programmable calculator is provided by employing a modular read-write and read-only memory unit capable of being expanded to provide the calculator with additional program and data storage functions oriented towards the environment of the user, a central processing unit capable of performing both serial binary and parallel binary-coded-decimal arithmetic, and an input-output control unit capable of bidirectionally transferring information between the memory or central processing units and a number of input and output units. The memory, central processor, and input-output control units are controlled by a microprocessor included in the central processing unit. A keyboard input unit with a plurality of sections capable of being defined by plug-in read-only memory modules and stored programs added by the user, a magnetic card reading and recording unit, a solid state output display unit, and an output printer unit are included among the input and output units.