OISC
From Esolang
OISC is the One Instruction Set Computer (by analogy with RISC and CISC), an esoteric machine providing only one instruction. In most implementations this instruction is subtract and branch unless positive, abbreviated subnp or subleq, or sometimes subtract and branch if negative (as in MISC), which only differ by zero-inclusion. Some implementations use a memory mapped instruction pointer and skip instead of branch (as in Subskin). Branching is done by writing to IP in these implementations. Another common instruction to use in OISC is move, in which case memory mappings are used to create other functionality, a form of system call.
The subtract-and-branch-unless-positive operation usually has three parameters. subleq(a,b,c) (Subleq) subtracts a from b, stores the result in b, and then transfers control to the address in c if the result was nonpositive. Some implementations allow a fourth parameter, in which case the result is not stored in one of the subtraction operands.
Both the subtract-and-branch and move implementations of OISC can be Turing-complete, making them Turing tarpits.
