Design and construction Colossus computer

stepping switch original colossus presented director of gchq director of nsa mark 40th anniversary of ukusa agreement in 1986

tommy flowers mbe senior electrical engineer , head of switching group @ post office research station @ dollis hill. prior work on colossus, had been involved gc&cs @ bletchley park february 1941 in attempt improve bombes used in cryptanalysis of german enigma cipher machine. recommended max newman alan turing, had been impressed work on bombes. main components of heath robinson machine follows.

a tape transport , reading mechanism ran looped key , message tapes @ between 1000 , 2000 characters per second.
a combining unit implemented logic of tutte s method.
a counting unit had been designed c. e. wynn-williams of telecommunications research establishment (tre) @ malvern, counted number of times logical function returned specified truth value.

flowers had been brought in design heath robinson s combining unit. not impressed system of key tape had kept synchronised message tape and, on own initiative, designed electronic machine eliminated need key tape having electronic analogue of lorenz (tunny) machine. presented design max newman in february 1943, idea 1 2 thousand thermionic valves (vacuum tubes , thyratrons) proposed, work reliably, greeted great scepticism, more robinsons ordered dollis hill. flowers, however, knew pre-war work thermionic valve failures occurred result of thermal stresses @ power up, not powering machine down reduced failure rates low levels. flowers persisted idea , obtained support director of research station, w gordon radley. flowers , team of fifty people in switching group spent eleven months february 1943 designing , building machine dispensed second tape of heath robinson, generating wheel patterns electronically. flowers used of own money project.

this prototype, mark 1 colossus, performed satisfactorily @ dollis hill on 8 december 1943 , taken apart , shipped bletchley park, delivered on 18 january , re-assembled harry fensom , don horwood. attacked first message on 5 february 1944. large structure dubbed colossus wrns operators. machine contained 1600 thermionic valves (tubes).

during development of prototype, improved design had been developed – mark 2 colossus. 4 of these ordered in march 1944 , end of april number on order had been increased twelve. dollis hill put under pressure have first of these working 1 june. first mark 2 colossus, containing 2400 valves, became operational @ 08:00 on 1 june 1944 after allen coombs took on leadership of colossus production. subsequently, colossi delivered @ rate of 1 month. time of v-e day there ten colossi working @ bletchley park , start had been made on assembling eleventh.

colossus 10 extended bedstead in block h @ bletchley park in space containing tunny galley of national museum of computing

the main units of mark 2 design follows.

a tape transport 8-photocell reading mechanism.
five 6-bit fifo shift registers.
twelve thyratron ring stores simulated lorenz machine generating bit-stream each wheel.
panels of switches specifying program , set total .
a set of function units performed boolean operations.
a span counter suspend counting part of tape.
a master control handled clocking, start , stop signals, counter readout , printing.
five electronic counters.
an electric typewriter.

most of design of electronics work of tommy flowers, assisted william chandler, sidney broadhurst , allen coombs; erie speight , arnold lynch developing photoelectric reading mechanism. coombs remembered flowers, having produced rough draft of design, tearing pieces handed out colleagues them detailed design , team manufacture it. mark 2 colossi both 5 times faster , simpler operate prototype.

the design overcame problem of synchronizing electronics message tape generating clock signal reading sprocket holes of message tape. speed of operation limited mechanics of reading tape. tape reader tested 9700 characters per second (53 mph) before tape disintegrated. 5000 characters/second (40 ft/s (12.2 m/s; 27.3 mph)) settled on speed regular use. flowers designed shift registers, 1 being used each of 5 channels of punched tape. shift register stored successive bits each of tape channels , delivered 5 successive characters (either z or Δz according switch selection) processors. five-way parallelism enabled 5 simultaneous tests , counts performed giving effective processing speed of 25,000 characters per second. computer used algorithms devised w. t. tutte , colleagues decrypt tunny message.