In the 1980s, pSOS rapidly became the RTOS of choice for all embedded systems based on the Motorola 68000 series family architecture, because it was written in 68000 assembly language and was highly optimised from the start.
It was also modularised, with early support for OS-aware debugging, plug-in device drivers, Internet protocol suite (TCP/IP) stacks, language libraries, and disk subsystems.
In July 1994, ISI acquired Digital Research's modular real-time multi-tasking operating system FlexOS from Novell.
In March 2000, rival company Express Logic released their Evaluation Kit for pSOS+ users, designed to provide a migration path to its ThreadX RTOS.
Compared to Linux, RTEMS is a closer match to pSOS applications due to its lower memory size and its strict realtime behaviour.