<P> In 1941, Zuse followed his earlier machine up with the Z3, the world's first working electromechanical programmable, fully automatic digital computer . The Z3 was built with 2000 relays, implementing a 22 bit word length that operated at a clock frequency of about 5--10 Hz . Program code was supplied on punched film while data could be stored in 64 words of memory or supplied from the keyboard . It was quite similar to modern machines in some respects, pioneering numerous advances such as floating point numbers . Rather than the harder - to - implement decimal system (used in Charles Babbage's earlier design), using a binary system meant that Zuse's machines were easier to build and potentially more reliable, given the technologies available at that time . The Z3 was Turing complete . </P> <P> Purely electronic circuit elements soon replaced their mechanical and electromechanical equivalents, at the same time that digital calculation replaced analog . The engineer Tommy Flowers, working at the Post Office Research Station in London in the 1930s, began to explore the possible use of electronics for the telephone exchange . Experimental equipment that he built in 1934 went into operation five years later, converting a portion of the telephone exchange network into an electronic data processing system, using thousands of vacuum tubes . In the US, John Vincent Atanasoff and Clifford E. Berry of Iowa State University developed and tested the Atanasoff--Berry Computer (ABC) in 1942, the first "automatic electronic digital computer". This design was also all - electronic and used about 300 vacuum tubes, with capacitors fixed in a mechanically rotating drum for memory . </P> <P> During World War II, the British at Bletchley Park achieved a number of successes at breaking encrypted German military communications . The German encryption machine, Enigma, was first attacked with the help of the electro - mechanical bombes . To crack the more sophisticated German Lorenz SZ 40 / 42 machine, used for high - level Army communications, Max Newman and his colleagues commissioned Flowers to build the Colossus . He spent eleven months from early February 1943 designing and building the first Colossus . After a functional test in December 1943, Colossus was shipped to Bletchley Park, where it was delivered on 18 January 1944 and attacked its first message on 5 February . </P> <P> Colossus was the world's first electronic digital programmable computer . It used a large number of valves (vacuum tubes). It had paper - tape input and was capable of being configured to perform a variety of boolean logical operations on its data, but it was not Turing - complete . Nine Mk II Colossi were built (The Mk I was converted to a Mk II making ten machines in total). Colossus Mark I contained 1,500 thermionic valves (tubes), but Mark II with 2,400 valves, was both 5 times faster and simpler to operate than Mark I, greatly speeding the decoding process . </P>

When were the first computers invented and used