The Atari Microsoft BASIC and Atari Microsoft BASIC II variants of the BASIC programming language were cartridge or floppy disk packaged versions of the Microsoft BASIC dialect ported to the Atari 8-bit machines.
Atari originally licensed Microsoft BASIC for use in their 8-bit computers, but were unable to fit it in an 8KB ROM cartridge, the largest at the time. They outsourced to another company, Shepardson Microsystems Inc., who created Atari BASIC instead.
Atari Microsoft BASIC, unlike Atari BASIC, didn't allow abbreviations for keywords. Keywords had to be fully spelled out. Syntax checking occurred after running a program, not immediately after entering the line. Also, arithmetic operations with integers resulted in an integer result.