The first to be demonstrated working was the Manchester Small-Scale Experimental Machine ( SSEM or `` Baby '' ) , while the EDSAC , completed a year after SSEM , was the first really useful computer that used the stored program design . The first working prototype to be demonstrated was the Manchester Small-Scale Experimental Machine ( SSEM or `` Baby '' ) in 1948 . The Electronic Delay Storage Automatic Calculator ( EDSAC ) , completed a year after the SSEM at Cambridge University , was the first practical , non-experimental implementation of the stored program design and was put to use immediately for research work at the university .