In 1967 IBM introduced a variant model of its System 360, the model 67. This machine was interesting in several respects. It was IBM’s first commercial system with dynamic memory mapping. It had 31 bit addresses where the rest of the 360 family had 24 bit addresses. It included an optional 2nd processor which shared physical core memory in what today is called symmetric multiprocessing. The model 67 could run IBM’s normal operating systems, TSS (which was delivered a couple of years later) or CP 67 which was a virtual machine product from IBM’s Cambridge MA office.

The duplex model 67 could also run “core wars” a game played a few times by a couple of programmers who would each have their program placed in memory at an address of their choosing. Each program was obeyed by one CPU initially in privileged mode. There was no memory protection initially and no sure way for a program to protect itself. To win was to get the opponent’s CPU to obey your program.