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A vacuum-tube computernow termed a first-generation computeris a computer that uses vacuum tubes for logic circuitry. While the history of mechanical aids to computation goes back centuriesif not millenniathe history of vacuum tube computers is confined to the middle of the 20th century. Lee De Forest invented the triode in The first example of using vacuum tubes for computation, the Atanasoff—Berry tuben farsta programwas demonstrated in Vacuum-tube computers were initially one-of-a-kind designs, but commercial models were introduced in the s and sold in volumes ranging from single digits to thousands of units.
By the early s vacuum tube computers were obsolete, superseded by second-generation transistorized computers. Much of what we now consider part of digital computing evolved during the vacuum tube era.
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Initially, vacuum tube computers performed the same operations as earlier mechanical computers, only at much higher speeds. Gears and mechanical relays operate in milliseconds, whereas vacuum tubes can switch in microseconds. The first departure from what was possible prior to vacuum tubes was the incorporation of large memories that could store thousands of bits of data and randomly access them at high speeds.
That, in turn, allowed the storage of machine instructions in the same memory as data—the stored program concept, a breakthrough which today is a hallmark of digital computers. The use of cross-coupled vacuum-tube amplifiers to produce a train of pulses was described by Eccles and Jordan in This circuit became the tuben farsta program of the flip-flopa circuit with two states that became the fundamental element of electronic binary digital computers.
The Atanasoff—Berry computera prototype of which was first demonstrated inis now credited as the first vacuum-tube computer.
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During World War II, special-purpose vacuum-tube digital computers such as Colossus were used to break German machine teleprinter ciphers known as Fish. The military intelligence gathered by these systems was essential to the Allied war effort. Also during the war, electro-mechanical binary computers were being developed by Konrad Zuse. The German military establishment during the war did not prioritize computer development.
An experimental electronic computer circuit with around tuben farsta programs was developed inbut destroyed in an air raid. The machine was completed in Although one application which motivated its development was the production of firing tables for artillery, one of the first uses of ENIAC was to carry out calculations related to the development of a hydrogen bomb. ENIAC was initially programmed with plugboards and switches instead of an electronically stored program.
Early machines which were used to tabulate punch cards could only add and subtract.
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Much faster than theit could divide and perform up to 60 program steps in one card cycle. Some units were leased or sold, making it the first successful commercial application of electronic computation. The Ferranti Mark 1 is considered the first commercial stored program vacuum tube computer. The first mass-produced computers were the Bull Gamma 31, units and the IBM2, units.
Vacuum-tube technology required a great deal of electricity.
The ENIAC computer had over 17, tubes and suffered a tube failure which would take 15 minutes to locate on average every two days. In operation the ENIAC consumed kilowatts of power, [ 3 ] of which 80 kilowatts were used for heating tubes, 45 kilowatts for DC power supplies, 20 kilowatts for ventilation blowers, and 5 kilowatts for punched-card auxiliary equipment. Because the failure of any one of the thousands of tubes in a computer could result in errors, tube reliability was of high importance.
Special quality tuben farsta programs were built for computer service, with higher standards of materials, inspection and testing than standard receiving tubes. One effect of digital operation that rarely appeared in analog circuits was cathode poisoning. Vacuum tubes that operated for extended intervals with no plate current would develop a high-resistivity layer on the cathodes, reducing the gain of the tube.
Specially selected materials were required for computer tubes to prevent this effect. To avoid mechanical stresses associated with warming the tubes to operating temperature, often the tube heaters had their full operating voltage applied slowly, over a minute or more, to prevent stress-related fractures of the cathode heaters. To avoid thermal cycling, heater power could be left on during standby time for the machine, with high-voltage plate supplies switched off.
Marginal testing was built into sub-systems of a vacuum-tube computer; by lowering plate or heater voltages and testing for proper operation, components at risk of early failure could be detected. To regulate all the power-supply voltages and prevent surges and tuben farsta programs from the power grid from affecting computer operation, power was derived from a motor-generator set that improved the stability and regulation of power-supply voltages.
Two broad types of logic circuits were used in construction of vacuum-tube computers. The "asynchronous", or direct, DC-coupled type used only resistors to connect between logic gates and within the gates themselves. Logic levels were represented by two widely separated voltages. In the "synchronous", or "dynamic pulse", type of logic, every stage was coupled by pulse networks such as transformers or capacitors.