Operating System Facilities

Most O/S support is for some form of communication and sharing of devices, and so has some facilities for building protocols. However, conventional device support usually assumes that devices are accessed over a local bus, and so are almost error free and with delays similar to memory access. Also, sharing of devices is achieved by access being only via a device driver, and is therefore easily achieved. The system safely separates users from each other, and protects devices from aberrant behavior of users processes by restricting access through system calls. A conventional multi-user operating system might be structured something like this: Within the Kernel, or in an Real Time System, the structuring is rather different with closer cooperation between processes or threads of control, less protection, and the assumption that the programmer is more expert.