First generation computers emerged during WW2 and developed in the 1950s and were based on quite different from the present technology: vaccum tubes/germanium diodes for processing and delay lines for memory. Running those ancestors is extremely difficult given the few examplaries left, their delicate technology and the lost expertise. However at a logical level, their architecture is not so different of our current computers as theses ancestors quickly adhered to the then emerging Von Neumann architecture. This allow us to understand their behaviour on programs through emulating their instruction set and memory structure. This talk presents this process applied by the NAM-IP computer museum to revive the memory of the GAMMA 3, the first french computer build and sold by Bull between 1952 and 1962. After describing the machine structure and some existing emulators (assembly/javascript from ACONIT), we show how to progressively build a JAVA implementation by following the actual machine evolution from a core machine centered on an ALU operating on 7 decimal words and a 64 instruction panel to an enriched instruction set supporting a binary computation mode and external memories, including a magnetic drum of about 100KB. We then demonstrate the result on a few business programs recovered from that era. The talk also reminds about key concepts, the electromecanical context and how the transition proceeded to computers.