In the same fashion as the PDP8, the ION instruction would delay one cycle, to allow execution of the indirect jump back, to avoid having to handle another interrupt while still in the interrupt service routine. Back to Top What operating systems were available?
Early machines, prior to the Mark 3 were not necessarily provided with any operating system – the programs would be designed to operate at fixed locations in memory. Most systems supplied included only a single screen, and one printer. If more than one screen was required, and the customer expected to run the same program on both screens, two versions of the code was supplied, each designed to operate at a different core address. LOS – Leicester Operating System The first recognisable operating system was produced in Leicester by Joe Templeman. in late 1974. “Version 1 of LOS was developed entirely by Joe Templeman specifically for a client called C Victor (Swimwear) who had ordered two 8 line CDC VDUs and I, as Midlands Software Manager, had said that I wanted them to be able to run any program from either VDU without having two copies of each program” – Chris Green’s recollection “Well, I joined BCL in May 1975 so my story begins a little while after that, as it took a little time to
