Input was still by simple keyboard to set store information directly, and output by inspection of CRT display tubes.
The Manchester Mark 1 was one of the first computers that could run a stored program. Built at the Victoria University of Manchester, the first version of the Mark 1 became operational in April 1949. It was used to run a program to search for Mersenne primes for nine hours without error on June 16 and 17 that same year.
The development of the Manchester Mark 1 ended the same year it became operational; giving way to the Ferranti Mark 1 computer. The Mark 1 computer implemented 34 new patents and the use of index registers, which allow programs to read through a set, or an array of words stored in the computer's memory.
Learn a brief history of computer at Computerhistory.org.