What Are Special Purpose Digital Computers?

Special Purpose Digital Computers were early forms of mainframes.

The term "Special Purpose Digital Computers" is an historical name, rarely used in modern computing. The early development of computers was driven by the need for machines to perform specific tasks, like decoding encryption or calculating complicated arithmetic. These special-purpose machines attracted funding that drove forward the development of computing. Digital computers began to emerge in the late 1930s and early 1940s.

Special Purpose Machines

The earliest special purpose computers were not what we would recognize as a computer today. The progression from machine to computer was gradual, and the precise dividing line between the two definitions is open to interpretation. Charles Babbage defined an "Analytical Engine" in 1837 which incorporated the use of punch cards to input instructions to the machine. The idea of punch cards for input came from the invention of a loom by Joseph Marie Jackard in 1801. The ability to program a machine, and the specific task of weaving cloth, makes the Jackard Loom an early form of special purpose computer. Punch cards as an input method continued to be used in computing up until the early 1970s.

Special Purpose Computers

Although programmable, Jackard's Loom and Babbagage's Analytical Engine (which was never actually built) stretch the definition of "computer." The development of electronic computers grew out of the research of John Atanasoff at Iowa State University in 1937. This large electrical device was much closer to our understanding of computers, and incorporated the interpretation of data as numbers, making it a "digital computer." This groundwork fed into the British "Colossus" project during the second world war. The Colossus computers were built specifically to decode the German cypher, called the "Enigma" code. For this reason, the Colossus is viewed as the first Special Purpose Digital Computer.

Electrical to Electronic

Early computers, like the Colossus, were built with a series of valves and capacitors which held binary numbers expressed as either on (1) or off (0). The expense and size of these early computers meant that they were only commissioned for specific tasks of national importance. The invention of microchips and integrated circuits through the 1950s and 1960s pushed computing into the electronic age. Once computers became cheaper to produce, they became general purpose machines, and so the concept of special purpose digital computers began to fade from common usage.

Modern Times

There are now many special purpose implementations of computing. Few electronic goods do not contain a microchip specifically hard-coded to handle the requirements of the equipment's function. However, these devices are "microprocessors" or "microcontrollers" and are never referred to as "digital computers." For this reason, the term "special purpose digital computer" is rarely used to refer to modern applications and computer-controlled goods.

References

• University of Liverpool: Mechanical Aids to Computation and the Development of Algorithms
• Newcastle University: The History of Digital Computers