7 Tom Kilburn 7designed and built the first stored-program computer
and led a team that produced a succession of pioneering
computers over the next 25 years.
In 1942 Kilburn graduated from the University of
Cambridge with a degree in mathematics. He immediately
converted, however, to electronics research when he was
recruited to join Frederic Williams’s wartime radar group
at the Telecommunications Research Establishment
(TRE). In December 1946 Williams left TRE to become a
professor at the University of Manchester, and Kilburn
accompanied him in order to help develop an electronic
storage system for electronic computers. They devised a
storage device—later known as the Williams tube—based
on cathode-ray tubes. A working model was completed
late in 1947, and by June 1948 they had incorporated it in a
small electronic computer that they built to prove the
device’s effectiveness. The computer was called the Small
Scale Experimental Machine (SSEM) or just “Baby.” It
was the world’s first working stored-program computer,
and the Williams tube became one of the two standard
methods of storage used by computers worldwide until
the advent of magnetic-core storage in the mid-1950s. By
April 1949 the SSEM had developed into a full-sized
machine, and by October 1949 secondary storage had
been added (using a magnetic drum). This machine, the
Manchester Mark I, was the prototype for the Ferranti
Mark I, manufactured by Ferranti, Ltd.
From 1951 Kilburn formally led the computer group
within Williams’s electrical engineering department. In
1953 the group completed an experimental computer using
transistors instead of vacuum tubes. In 1954 the group
completed MEG, which provided floating-point arithme-
tic (calculations using exponential notation—e.g., 3.27 ×
1017 ) and was manufactured by Ferranti as the Mercury
beginning in 1957.