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Section 4

Desk calculator computers: keyboard programmable processors with small memories

These stored program computers have interesting features. For example, the keyboard is utilized several ways:

1 T.console mode; a conventional console for entering data in response to a stored program

2 Program entry mode; a device for creating stored programs

3 Desk calculator mode; a part of the arithmetic (data) element by issuing direct instructions and thus obtaining results directly independent of a program

Uses 2 and 3 are both internally and externally programmed. The data types are decimal (both fixed and floating) because of the intimate interface they require to the user. Some calculators interpret nested (parenthesized) algebraic expressions.

These calculators easily meet the definition for a stored-program computer. It is apparent their designers know a great deal about general purpose stored-program computers. The machines are cleverly designed and make efficient use of the hardware they possess. Eventually there may be more of these computers than conventional stored program computers. The reader should note that not all "electronic desk calculators" are computers; most are electronic versions of their mechanical or electromechanical ancestors.


The Programma 101 (Chap. 19) is at the limit of what we call a stored program computer. It has a sufficient instruction set to be classified as a computer, but the storage for temporary data, constants, and programs is limited. The machine's instruction set is interesting because memory is not addressed explicitly. A jump, for example, is executed by scanning the program for a particular marker which was named in the jump instruction. The Programma 101 uses an Mp.cyclic.

The program library for the Programma 101 is extensive and provides an indication of its capability.

The Hewlett-Packard Model 9100A computing calculator

The HP 9100A (Chap. 20), like the Programma 101 (Chap. 19), is a desk calculator. They are both stored program computers. Programma is designed for simpler accounting and statistical-tabulation tasks and has fixed-point decimal data. (Programma 101 costs somewhat less.) The HP 9100A operates on both fixed-and floating-point decimal data with scalar, rectangular, and polar coordinate vectors and is designed for engineering and scientific calculations. Thus, according to a measure based on data types and operators, the HP 9100A is about the most complete computer in the book. Its operations are given in the PMS diagram of Fig. 1.

Fig. 1. Hewlett-Packard Model 9100A Computing Calculator PMS diagram.


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