Optimized Systems Software

Optimized Systems Software

Optimized Systems Software (OSS) was a small company that produced disk operating systems and programming languages for primarily the Atari 8-bit computers. OSS is best known for their enhanced versions of Atari BASIC, the MAC/65 assembler (which is much faster than Atari’s products), and the Action! programming language.

Atari 8-bit products


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.

  • OS/A+ 2.0, 2.1 was a disk-based replacement for the Atari DOS and the Apple II DOS. It replaced the menu-driven utilities with a compact command line approach similar to CP/M (and later, DOS). The command line was small enough to remain in memory with most applications, removing the need for the dreaded post-program reload. When first introduced at the West Coast Computer Faire, the program was named CP/A, but a lawyer from Digital Research (owners of CP/M) visited the booth and the name was changed. OSS couldn’t have afforded even a court filing fee.
  • OS/A+ 4.1 OSS extended the successful OS/A+ product with additional capabilities for version 4, many of which were arguably ahead of their time. For example, the strict “8.3” naming scheme (eight alphanumeric characters with a three character extension) was replaced by “long” filenames, similar to the Microsoft DOS transition toVFAT in 1995.

However, unlike VFAT, OS/A+ 4.1 disks were not backward compatible with earlier systems; Atari DOS or OS/A+ 2.1 could not read disks formatted by OS/A+ 4.1, breaking backward compatibility. The memory footprint was larger as well, resulting in insufficient memory to run some popular applications. As a result of these drawbacks, OS/A+ 4.1 did not achieve the market penetration as the earlier product. OSS did reissue OS/A+ 4.1 for a brief period when they decided not to modify DOS XL for double-sided disk support.


DOS XL was designed to replace OS/A+. Included support for single and double-density disk drives. Utilized the command-prompt of OS/A+ but also included a menu program. Featured extensions that took advantage of unused memory space in Atari XL/XE computers and OSS supercartridges. Included support for Indus GT Synchromesh. Due to lack of demand and Atari working on a new version of DOS, OSS decided to halt development of DOS XL 4 and reissue OS/A+ version 4.1.


Atari BASIC had been designed to fit in a single 8K cartridge, with an optional second cartridge adding additional capability (the Atari 800 home computer featured two cartridge slots). However, the second cartridge was never produced. Instead, OSS produced a disk-based product called BASIC A Plus (or BASIC A+), which was compatible with Atari BASIC but corrected several bugs and added quite a few features. Among the notable features were PRINT USING (for formatted output), trace and debug enhancements, direct DOS commands, and explicit support for the Atari computers’ exceptional graphics hardware.

Because BASIC A+ had to be purchased, programs developed using its extended features could not be shared with people who did not own the interpreter.


A bank-selected cartridge version of the language that replaced BASIC A+. It fixed bugs and added even more commands and features. The BASIC XL Toolkit contains additional code and examples for use with the BASIC XL language. Included a runtime package for redistribution. No compiler was available.


An enhanced version of the BASIC X bank-selected cartridge,with additional functions and high-speed math routines. Because it required 64KB, it would only run on an XL/XE system. No compiler or runtime was made available. The BASIC XL runtime could be used, but restricted to only XL functions.


A cartridge-based development system for a readable ALGOL-like language that compiles to efficient 6502 code. Action! combines a full-screen editor with a compiler that generates code directly to memory without involving disk access. The language found a niche for being over a hundred times faster than Atari BASIC, but much easier to program in than assembly language. Compiled Action! programs require the cartridge to be present—because standard library functions are on the cartridge—unless the developer uses the Run Time Package (which was a separate purchase).

The Action! Toolkit (originally called the Programmer’s Aid Disk, or PAD) contains additional code and examples for use with the Action! language. The Action! Run-Time Package allows Action! programs to be redistributed to Atari users without the Action! cartridge.


EASMD (Edit/ASseMble/Debug) is the first editor/assembler from OSS. Based on the original Atari Assembler Editor, it was released in 1981 on disk. It was superseded by MAC/65.


MAC/65 is 6502 editor/assembler originally released on disk in 1982, then on a bank-switched “supercartridge” in 1983 which included an integrated debugger (DDT). Like Atari BASIC, MAC/65 used line-numbered source code and tokenized each line as it was entered. It was significantly faster than Atari’s assemblers. The MAC/65 Toolkit disk contains additional code and examples.


A machine language debugger. It was initially included with MAC/65, but the cartridge-based version of the assembler added its own debugger, DDT. BUG/65 was later added to DOS XL.


A compiler for a subset of the C programming language. C/65 only generated assembly source code. An assembler like MAC/65 was needed to generate an executable file.

The Writer’s Tool

A word processing application available in a bank-selected cartridge and a double-sided disk (master disk on one side, dictionary disk on the other side). It was developed by Madison Micro and published by OSS in 1984. According to Bill Wilkinson, OSS was already building a word processor, but stopped when The Writer’s Tool was submitted.