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linked from that page:

""" The University of Manchester's Small-Scale Experimental Machine (SSEM)[15] is generally recognized as world's first electronic computer that ran a stored program—an event that occurred on 21 June 1948.[16][17] However the SSEM was not regarded as a full-fledged computer, but more a proof of concept predecessor to the Manchester Mark 1 computer, which was first put to research work in April 1949. On 6 May 1949 the EDSAC in Cambridge ran its first program, making it arguably "the first complete and fully operational regular electronic digital stored-program computer".[18] It is sometimes claimed that the IBM SSEC, operational in January 1948, was the first stored-program computer;[19] this claim is controversial, not least because of the hierarchical memory system of the SSEC, and because some aspects of its operations, like access to relays or tape drives, were determined by plugging.[20] """

https://en.wikipedia.org/wiki/Stored-program_computer