The Computer History Museum released the source code for the 1969-1972 “XM6” version of APL for the System/360 mainframe, available now for non-commercial use. Developed from Kenneth Iverson’s 1957 mathematical notation, APL focused intensely on array processing, diverging sharply from general-purpose languages of the era.

Iverson, originally a Harvard professor, formalized his notation at IBM after joining in 1960. APL360 became popular because it offered a complete interactive programming environment via timesharing, allowing immediate feedback from electromechanical typewriters. This version was written entirely in 360 assembly language, essentially bundling the OS with the high-level language.

APL’s technical distinctions included right-to-left evaluation without function precedence hierarchy and automatic vector/array creation, encouraging developers to use high-dimensional temporary structures. The system required specialized keyboards due to its unconventional, mathematics-like symbols, such as ÷ for division instead of /, making mastery a substantial effort.

Jürgen Winkelmann at ETH Zürich has already adapted this archival material into a runnable system, MVT for APL Version 2.00. This release provides engineers a direct look into a historically unique approach to computation and language design.