An adaptable programmable calculator is provided by employing modular read-write and read-only memory units capable of being expanded to provide the calculator with additional program and data storage functions, a central processing unit, and an input-output control unit for 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. The input and output units include a keyboard input unit, a magnetic card reading and recording unit, a solid state multi-character display unit capable of displaying every alphabetic and numeric character and many other symbols individually and in a line of one or more alphameric statements, and a thermal printer unit. The keyboard input unit includes a plurality of definable keys by which the user may define and store in the read-write memory unit additional keyboard functions to be performed by the calculator, may associate each such defined keyboard function with a separate definable key of the keyboard, and may cause each such defined keyboard function to be executed and/or stored as part of a program, either by itself or as part of an arithmetic expression. Additional keyboard functions defined by the user and stored within the calculator read-write memory may include parameters that have been specified by the user and that may include input data comprising numerical data, storage register designations, output register designations, and arithmetic expressions. Subroutines may be defined by the user, stored in the calculator read-write memory, and associated with a separate definable key of the keyboard and may include the specification of local and global variables.