Withdrawn Standard. Withdrawn Date: Apr 28, 1996. No longer endorsed by the IEEE. Describes the IEEE Std 855-1990, IEEE standard for microprocessor operating system interfaces (MOSI), which defines an interface between application programs and their operating environments. It is designed to be compatible with most operating systems in common use in microcomputer environments, within the scope of services that the various operating systems provide. It can be used to access the services of a variety of operating systems in both small-scale and large-scale environments.