|Company / developer||Alfred Chao / SCG / ISI / Wind River Systems|
|Programmed in||68000 assembler|
|OS family||Real-time operating systems|
|Source model||Closed source|
|Marketing target||Embedded systems|
|Supported platforms||Motorola 68000|
pSOS (Portable Software On Silicon) is a real time operating system (RTOS), created in about 1982 by Alfred Chao, and developed/marketed for the first part of its life by his company Software Components Group (SCG). In the 1980s pSOS rapidly became the RTOS of choice for all embedded systems based on the Motorola 68000 family architecture, because it was written in 68000 assembler and was highly optimised from the start. It was also modularised, with early support for OS-aware debugging, plug-in device drivers, TCP/IP stacks, language libraries and disk subsystems. Later came source-level debugging, multi-processor support and further networking extensions.
In about 1991, Software Components Group was acquired by Integrated Systems Inc. (ISI) who further developed pSOS - now restyled pSOS+ - for other microprocessor families, by rewriting the greater part of it in C. Attention was also paid to supporting successively more integrated development environments, culminating in pRISM+.
In 1999 Integrated Systems Inc. was acquired by Wind River Systems, the originators of rival RTOS VxWorks. Despite initial reports that pSOS support would continue, development was halted. Wind River announced plans for a 'convergence' version of VxWorks which will support pSOS system calls, and that no further releases of pSOS itself will be made.
 Migration away from pSOS
In August 2007, RoweBots, a former partner of SCG and ISI, open sourced their pSOS+ compatible version called Reliant. It is available to all that wish to upgrade without applications changes.
The Xenomai project supports pSOS+ APIs (and others traditional RTOS APIs) over a Linux-based real-time framework to allow existing industrial applications to migrate easily to a GNU/Linux-based environment while keeping stringent real-time guarantees.
 See also
- Express Logic announcement of their Evacuation Kit, retrieved 2007-06-13