Following on from my popular blog post about coding by hand in 1985 I dug into my pile of old stuff to look at how myself and another boy at school reverse engineered the Research Machines CHAIN network and built everything from networking protocols to a network management system in assembly language. In 1982 Research Machines in the UK launched the LINK 480Z Z80 based machine that had an optional 800kbps proprietary network called CHAIN . My upper school got a small network of them linked to a file server running MP/M . The 480Z's would boot from the file server across the network. Unfortunately, the entire network protocol was undocumented by Research Machines and unpublished. Myself and another boy, P, decided to reverse engineer because we wanted boot control and we wanted network access. Disassembling the running operating system (often using its front panel , which was on screen and not via flashing lights) we were able to determine that the Z80 RST 8 instruction