In computing, URISC is a machine in which there is only one instruction: reverse-subtract and skip if borrow. This is similar to the 'subtract and branch unless positive' operation from OISC.

Quoted from the author's initial email/posting:

The accumulator is subtracted from the memory location and the next instruction is skipped if there was a borrow. The result is stored in both the accumulator and the memory location. The PC is memory location 0.

The PC is the program counter (also known as the IP or instruction pointer).

The original work on this package was done by Mike Albaugh of Atari Games.

How to do something

By 'borrow' this assumes that the memory location was smaller than the accumulator.

Temp is a temporary memory location.

To set x to the value of y minus z (There may be a faster way.):

RSSB x

RSSB x

RSSB x

RSSB z

RSSB x

RSSB temp

RSSB temp

RSSB temp

RSSB temp

RSSB y

RSSB temp

RSSB temp

RSSB x

RSSB temp

RSSB temp

RSSB temp

RSSB temp

Reference

The Retrocomputing Museum