BASIC A+ is an implementation of the BASIC programming language for Atari 8-bit computers introduced by Optimized Systems Software in 1981. It was developed by the team that created Atari BASIC, which shipped with each computer, and is compatible. BASIC A+. BASIC A+ adds new features to the language, such as <code>IF..ELSE..ENDIF</code> statements, support for hardware features like player/missile graphics, and commands for debugging. While Atari BASIC is an 8 KB ROM cartridge, BASIC A+ is floppy disk based and uses 15 KB of the computer's RAM, leaving 23 KB available for user programs in a 48 KB Atari 800. BASIC A+ shipped with a supplement to the Atari BASIC reference manual as its documentation.
Optimized Systems Software followed BASIC A+ with the cartridge-based BASIC XL, then BASIC XE.