It was programmed by Kathleen O'Brien of Shepardson Microsystems, the company which wrote Atari BASIC, and Assembler Editor shares many design concepts with that language implementation.
Despite the recommendation, commercial software was written using the Assembler Editor, such as the games Eastern Front (1941),[2] Caverns of Mars,[3] Galahad and the Holy Grail,[4] and Kid Grid.
[5] The source code to the original Assembler Editor was licensed to Optimized Systems Software who shipped EASMD based on it.
Like Atari BASIC, Assembler Editor includes an ENTER command that can be used to combine files together into a single larger program listing.
[8] Variable names can be assigned to specific addresses, and this was often combined with an increment *= *+1 to directly encode offsets into tables.
[17] As part of Shepardson's work, a number of common routines were incorporated into the Atari computer's operating system, including the floating point math functions.
[17] The low performance of key functions affected both Atari BASIC and the Assembler Editor and was a topic that Wilkinson often wrote about.
[19] O'Brien, Laughton, and Wilkinson formed their own company, Optimized Systems Software (OSS), to continue development of the Atari products.
They licensed the original source code for BASIC, Assembler Editor, and Atari DOS, which they had collectively written.
[13] Much of the improved performance of MAC/65 is the result of tokenizing lines of code as they're entered—as is the case with Atari BASIC—to reduce the amount of work needed at assembly time.