First German Sequence-Controlled Electronic Digital Calculator. Physicist Heinz Billing¹ at the controls of his newest invention, the G1 calculator with Wilhelm Hopmann checking for a loose tube socket. The G1 was a mostly electronic vacuum tube based machine he built by June 1952 at the Arbeitsgruppe Numerische Rechenmaschinen (Working Group on Numerical Calculators) Max Planck Institute for Physics in Göttingen, Germany. Powered by 476 vacuum tubes and 101 mechanical relays consuming 2.4 kW, the 7.2 kHz machine had a slow speed of 3 operations/sec because of the bottleneck imposed by the use of mechanical relay components. It was 32-bit serial calculator with only 36 words stored on an tiny 8″ drum memory spinning at 3000 rpm with 9 read/write heads, the drum storing variables only so the machine had a Harvard architecture. The calculator was controlled entirely by programs on four selectable punched tapes, all the contents of each single track on the drum can be shifted cyclica.