'''pSOS''' ('''''P'''ortable '''S'''oftware '''O'''n '''S'''ilicon'') 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 as pSOS+ - for other microprocessor families, by rewriting the greater part of it in C. Attention was also paid to supporting successively more [[integrated development environment]]s, culminating in pRISM+.
