Notable early computing devices

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Notable early computing devices are computing devices which marked significant steps on the road from primitive computing devices (such as mechanical adding machines) to computers. The list below are the ones which the author of this page deems the most significant ones.

Depending exactly how one defines 'computer', some of these might have been computers. If a computer has to be able to modify its own program, none of these qualify. If it has to have the ability to do conditional branches, those were added to the Automatic Sequence Controlled Calculator and Zuse Z4 later in their lives.

Non-electronic early computing devices

Some of the first powerful computing devices were those of Charles Babbage. A prototype of the first, the Difference Engine (an idea originated by Johann Helfrich von Müller in 1786) was started in the 1820's, but never finished. (The Science Museum recently built an actual Difference Engine, using a better design he created in 1847-49, but never attempted to build; it worked reasonably well.) His later proposed Analytical Engine (conceived in the 1830's; prototyping begun in the 1860's) was the first programmable computing device, and a general-purpose one, but its program was fixed (in read-only memory, effectively). His engines were all digital, but entirely mechanical.

Vannevar Bush created his Differential Analyzer at MIT in 1928–1931; it was an analog device, mostly mechanical. Many similar machines were then created in the US, UK, Norway, etc; this created an environment in which people were used to using complex computing devices to solve problems, and thus laid the ground for true computers. In some ways, it created the environment for the creation of Whirlwind (an important early computer).

Howard Aiken, inspired by Babbage's work, began the design of his ASCC in 1937; actually completed and used, it was a large programmable (but not alterable stored-program) electro-mechanical general-purpose digital computing device. Later successors from IBM were entirely relay-based, not partially mechanical, as the ASCC was; and eventually (in the Selective Sequence Electronic Calculator) partly electronic. Very slightly later than the ASCC, the Bell Telephone Laboratories relay computing devices of George Stibitz were also entirely relay-based, and digital.

Electronic computing devices

At about the same time as the ASCC, in 1938, John Vincent Atanasoff took the next step, and began the creation of the first electronic digital computing device, later called the Atanasoff-Berry Computer. It was not at all programmable or general-purpose; it could only solve systems of simultaneous equations. It was notable for having inspired John Mauchly to use a digital electronic approach when he later set out to build the ENIAC; and also for being the first digital electronic computing device to use capacitor-based memory - an approach to memory now ubiquitous in the Dynamic RAM of all modern computers.

The Colossus digital electronic code-breaking devices of Tommy Flowers, built in the UK during World War Two (construction of the first one started in 1943), were notable because they showed that large electronic computing devices could be made to operate reliably; because quite a few were produced; and because many of the post-War computer pioneers in the UK learned about the suitability of electronics for digital computing devices from them. They are often described as 'programmable', but this is incorrect - they had no program of any form, and they were not general-purpose; a better description is 'configurable'.

Effectively the last step before true computers was the ENIAC, a large digital electronic computing device. As originally designed, it was only configurable, requiring considerable effort to re-configure it to perform a different computation (although it was general-purpose, unlike the Atanasoff–Berry Computer and Colossus). In 1947 an effort was started to re-configure it in a way that added a certain amount of programmability, via a program stored in the 'function-table switches' (originally intended as a ROM data source). Later, minor hardware modifications improved ENIACs efficiency when configured as a stored-program machine; it started to operate in that mode in 1948.

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