GS/OS is an operating system designed by Apple Computer for their Apple IIGS personal computer. It provides facilities for accessing the file system, controlling input/output devices, and a system to handle interrupts and signals. It uses ProDOS as its primary filing system. GS/OS is a component of Apple IIGS System Software versions 4.0 to 6.0.1, and was the first true 16-bit operating system for the Apple IIGS.[1]