THE HISTORY OF COMPUTERS AND CALCULATORS

by

R. J.. Reiman, Historian

What is a computer? What is a calculator? For centuries, a computer designated a person who did calculations for a living. Its meaning has changed to mean a information processing machine which can store data (numbers, letters, pictures, symbols etc.) and can manipulate that data according to a program that is stored in the machine or processor. A computer is said to have the capacity to make decisions, such as a conditional jump, based on the results of its own computations. A computer possesses 5 basic parts, a central processor, central control, memory, and input and output units.

A calculator is defined as a small machine which does arithmetic, mathematical problems, and its operation must be directed every step of the way. Unable to store data and programs, it cannot make decisions.

The analytical engine of Charles Babbage in the 1880s resembled a calculator since it could only perform mathematical work and could not store programs. It also resembled a computer, since it was programmable, could do many thing automatically, and had a modest ability to make decisions. It had a memory (a store), a central processor (a mill) and a control (the barrel). Today, we would call it a program-controlled calculator. It did not have a stored program, and its instructions were limited to punch cards and tapes.

Was ENIAC, which was electric, could add 5,000 numbers in one second, and was a differential calculator, a computer in the sense of the above definition? Like the analytical engine, ENIAC was a program-controlled calculator. It had high speed, was programmable, and was general purpose, and a thousand times faster than its predecessors. It had no stored program, but it was truly revolutionary in 1944.

EDVAC, also the work of J. Presper Eckert Jr. and John W. Mauchly, included a stored-program, a central processor and a memory for both data and programs. An early decision was to store both program and data in the same memory and depend upon the rules of Boolean algebra and encoding to tell them apart. EDVAC had the advantage that the program could be modified, not with hard wiring, but by modifying the instructions {software}. Also, a library of programs could be stored and be accessible to meet various contingencies.

Operating at electronic speed, EDVAC could call up and carry out one program after another, and additionally it could apportion its memory space between data and programs according to need. Due to all kinds of internal interferences, delays, arguments, and even muddying of the credit to Eckert and Mauchly, the EDVAC project wasn't finished until 1952.

In Britain, Max Newman and F.C. Williams, building on the British electronic decoders of WWII, benefitted from a report on ENIAC and EDVAC written by John von Neumann. They were building MARK 1 at Manchester University.

The distinction of developing the first stored-program computer was Great Britain's with the MARK 1 in June 1948. This machine was later developed into the world's first commercial computer, the Ferranti MARK 1, which was delivered to customers in 1951, five months ahead of the UNIVAC which had been developed out of the ENIAC project.