Electromechanical versus Electronic Computation (The Modern History of Computing)

Electromechanical versus Electronic Computation

With some exceptions — including Babbage's purely mechanical engines, and the finger-powered National Accounting Machine - early digital computing machines were electromechanical. That is to say, their basic components were small, electrically-driven, mechanical switches called ‘relays’. These operate relatively slowly, whereas the basic components of an electronic computer — originally vacuum tubes (valves) — have no moving parts save electrons and so operate extremely fast. Electromechanical digital computing machines were built before and during the second world war by (among others) Howard Aiken at Harvard University, George Stibitz at Bell Telephone Laboratories, Turing at Princeton University and Bletchley Park, and Konrad Zuse in Berlin. To Zuse belongs the honour of having built the first working general-purpose program-controlled digital computer. This machine, later called the Z3, was functioning in 1941. (A program-controlled computer, as opposed to a stored-program computer, is set up for a new task by re-routing wires, by means of plugs etc.)

Relays were too slow and unreliable a medium for large-scale general-purpose digital computation (although Aiken made a valiant effort). It was the development of high-speed digital techniques using vacuum tubes that made the modern computer possible.

The earliest extensive use of vacuum tubes for digital data-processing appears to have been by the engineer Thomas Flowers, working in London at the British Post Office Research Station at Dollis Hill. Electronic equipment designed by Flowers in 1934, for controlling the connections between telephone exchanges, went into operation in 1939, and involved between three and four thousand vacuum tubes running continuously. In 1938–1939 Flowers worked on an experimental electronic digital data-processing system, involving a high-speed data store. Flowers' aim, achieved after the war, was that electronic equipment should replace existing, less reliable, systems built from relays and used in telephone exchanges. Flowers did not investigate the idea of using electronic equipment for numerical calculation, but has remarked that at the outbreak of war with Germany in 1939 he was possibly the only person in Britain who realized that vacuum tubes could be used on a large scale for high-speed digital computation. (See Copeland 2006 for m more information on Flowers' work.)

Atanasoff

The earliest comparable use of vacuum tubes in the U.S. seems to have been by John Atanasoff at what was then Iowa State College (now University). During the period 1937–1942 Atanasoff developed techniques for using vacuum tubes to perform numerical calculations digitally. In 1939, with the assistance of his student Clifford Berry, Atanasoff began building what is sometimes called the Atanasoff-Berry Computer, or ABC, a small-scale special-purpose electronic digital machine for the solution of systems of linear algebraic equations. The machine contained approximately 300 vacuum tubes. Although the electronic part of the machine functioned successfully, the computer as a whole never worked reliably, errors being introduced by the unsatisfactory binary card-reader. Work was discontinued in 1942 when Atanasoff left Iowa State.

Colossus

The first fully functioning electronic digital computer was Colossus, used by the Bletchley Park cryptanalysts from February 1944.

From very early in the war the Government Code and Cypher School (GC&CS) was successfully deciphering German radio communications encoded by means of the Enigma system, and by early 1942 about 39,000 intercepted messages were being decoded each month, thanks to electromechanical machines known as ‘bombes’. These were designed by Turing and Gordon Welchman (building on earlier work by Polish cryptanalysts).

During the second half of 1941, messages encoded by means of a totally different method began to be intercepted. This new cipher machine, code-named ‘Tunny’ by Bletchley Park, was broken in April 1942 and current traffic was read for the first time in July of that year. Based on binary teleprinter code, Tunny was used in preference to Morse-based Enigma for the encryption of high-level signals, for example messages from Hitler and members of the German High Command.

The need to decipher this vital intelligence as rapidly as possible led Max Newman to propose in November 1942 (shortly after his recruitment to GC&CS from Cambridge University) that key parts of the decryption process be automated, by means of high-speed electronic counting devices. The first machine designed and built to Newman's specification, known as the Heath Robinson, was relay-based with electronic circuits for counting. (The electronic counters were designed by C.E. Wynn-Williams, who had been using thyratron tubes in counting circuits at the Cavendish Laboratory, Cambridge, since 1932 [Wynn-Williams 1932].) Installed in June 1943, Heath Robinson was unreliable and slow, and its high-speed paper tapes were continually breaking, but it proved the worth of Newman's idea. Flowers recommended that an all-electronic machine be built instead, but he received no official encouragement from GC&CS. Working independently at the Post Office Research Station at Dollis Hill, Flowers quietly got on with constructing the world's first large-scale programmable electronic digital computer. Colossus I was delivered to Bletchley Park in January 1943.

By the end of the war there were ten Colossi working round the clock at Bletchley Park. From a cryptanalytic viewpoint, a major difference between the prototype Colossus I and the later machines was the addition of the so-called Special Attachment, following a key discovery by cryptanalysts Donald Michie and Jack Good. This broadened the function of Colossus from ‘wheel setting’ — i.e., determining the settings of the encoding wheels of the Tunny machine for a particular message, given the ‘patterns’ of the wheels — to ‘wheel breaking’, i.e., determining the wheel patterns themselves. The wheel patterns were eventually changed daily by the Germans on each of the numerous links between the German Army High Command and Army Group commanders in the field. By 1945 there were as many 30 links in total. About ten of these were broken and read regularly.

sumber:
http://plato.stanford.edu/entries/computing-history/