death code n.
A routine whose job is to set everything in the computer --
registers, memory, flags, everything -- to zero, including that
portion of memory where it is running; its last act is to stomp
on its own "store zero" instruction. Death code isn't very
useful, but writing it is an interesting hacking challenge on
architectures where the instruction set makes it possible, such
as the PDP-8 (it has also been done on the DG Nova).
Perhaps the ultimate death code is on the TI 990 series, where
all registers are actually in RAM, and the instruction "store
immediate 0" has the opcode "0". The PC will immediately wrap
around core as many times as it can until a user hits HALT. Any
empty memory location is death code. Worse, the manufacturer
recommended use of this instruction in startup code (which would
be in ROM and therefore survive).