The operating system is the TOS for The Operating System (officially) or 'Tramiel Operating System', after the name of Jack Tramiel.
The system is derived from the GEM graphical OS (with windows and mouse) created by Digital Research (creator of CP / M) for platforms such as Intel or Motorola. It was delivered in particular Amstrad PCs until Apple makes its marketing ban on PC platform for a dark story of trash icon. Microsoft has not yet released a Windows version exploitable, but worked hand in hand with Apple for porting Multiplan-Dos to Exel-Mac, and found himself and shed its dangerous competitor (and model) while Apple continues to Atari see it crop up its market to the bottom. The slogan for the Atari Tramiel STF was "The Power without the Price", especially as one of the first emulators was Magic-Sac / Spectrum 128 and GCR (developed by Dave Small, one of programmers most active of the scene Atari), Atari emulator for Mac is targuant of video performance 30% higher.