An adaptable programmable calculator is provided by employing modulr read-write and read-only memory units 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, 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 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 printer unit capable of printing on thermally sensitive paper every alphabetic and numeric character and many other symbols individually and in alphameric statements or messages. A printed listing of the line number and content of each line of one or more alphameric statements stored as part of a program in the read-write memory unit may be obtained by means of a LIST control key of the keyboard input unit. The user may also obtain, directly or as part of any program listing, a printed indication of the number of nondedicated storage registers within the calculator read-write memory that are currently available to the user for information storage.