A-0 System

The A-0 system (Arithmetic Language version 0) was an early tool for the first electronic computers. It was made by Grace Murray Hopper in 1951 and 1952 for the UNIVAC I computer.

The A-0 system worked differently from compilers today. It acted more like a loader or linker. People wrote programs by listing subroutines and their arguments, each with a number code. The A-0 system turned these lists into machine code the computer could run.

After the A-0, more advanced versions were created, like the A-1, A-2, A-3 (called ARITH-MATIC), AT-3 (called MATH-MATIC), and B-0 (called FLOW-MATIC). The A-2 system, made in 1953 at the UNIVAC division of Remington Rand, was shared with customers. They could even send back improvements. This sharing of code was like today’s free and open-source software, showing how early computer users worked together.