Optimized Systems Software was formed in early 1981 by Bill Wilkinson and Mike Peters, who had purchased Atari BASIC, Atari DOS and the Atari Assembler Editor product from Shepardson Microsystems, Inc. (SMI) who had concluded that their BASIC and DOS products were not viable. The new company enhanced the products, renaming them OS/A+ (the Disk Operating System), BASIC A+ (a disk-based language), and EASMD (a powerful assembler / editor). OSS continued to work with Atari (who had previously contracted with SMI) on enhanced products, most of which never reached the market.
OSS debuted at the West Coast Computer Faire, March 1981. Their products released over the next several years became respected among Atari programmers, particularly the MAC/65 assembler, the Action! programming language, and BASIC XL.
Atari DOS 2.0S consisted of two portions, a memory-resident portion that facilitated access to disk files by programs, and a disk-resident portion providing menu-driven utilities to format, copy, delete, rename, and otherwise manipulate files on Atari's 810 disk drive. The menu system was too large to keep memory-resident, but the necessity to reload the menu system after every program was frustrating to many users.