Both Colossus and ENIAC were programmed by rewiring them andsetting switches. The concept of storing a program in memory ascoded numeric instructions did not yet exist.All computing machines of the time were either programmed thisway or by reading instructions from punched tape. Readinginstructions from punched tape was OK for electromechanicalmachines (e.g. Harvard Mark I) but much too slow for the high speedall electronic machines (i.e. Colossus and ENIAC) that operated atspeeds of many thousands of operations per second. The idea ofstoring a program in memory came up while building ENIAC, but wasnot acted on until after the end of the war.Also the memorytechnology available at the time had neither the capacity nor thespeed needed to make it suitable for storing programs.Colossus read its data from punched tape as fast as was possibleto read it without having the paper shred itself (5000 charactersper second) and the Mark II version used a 5 level deep pipelineallowing the machine to process 25000 characters per second withparallel processing methods.The first computer to use a program stored in memory was theManchester Baby built in 1948, but its memory was only 32 words of32 bits each made with a CRT DRAM called a "William's Tube". Thismachine was a proof of concept prototype that led to later morepowerful computers.