Core War

At the start of a match, each warrior is loaded into a random memory location. Programs take turns executing one instruction at a time. A program wins by terminating all opponents, typically by causing them to execute invalid instructions, leaving the victorious program in sole possession of the machine.

Early versions of Redcode featured only eight instructions. This number increased to 10 in the ICWS-86 standard, 11 in ICWS-88, and 16 in the 1994 draft standard, which is still widely used. With various addressing modes and instruction modifiers introduced in the 1994 draft, the total number of possible operations is 7168. Redcode does not define how instructions are represented in memory, nor does it allow programs to inspect their own code structure beyond copying and equality comparisons. Arithmetic operations are limited to the instruction’s two address fields.

Core War was inspired by a self-replicating program called Creeper and a subsequent program called Reaper that destroyed copies of Creeper. Creeper was created by Bob Thomas at BBN. Dewdney was not aware of the origin of Creeper and Reaper and refers to them as a rumor originating from Darwin and the worm experiments of Shoch and Hupp. The 1984 Scientific American article on Core War nevertheless cites the game Darwin, created by Victor A. Vyssotsky, Robert Morris, and Douglas McIlroy at Bell Labs in 1961.

The word "Core" in the name comes from magnetic-core memory, an obsolete random-access memory technology. This term was then, and still today, typically in use as the term for working memory in working memory dumps, called core dumps, on Unix and most Unix-like systems. Additionally, the default filename used for core dumps on such systems is usually "core" or contains the word core.