The role and responsibilities of an OS

• manage and arbitrate access to hardware resources - CPU, memory, devices

• manage and arbitrate access to software abstractions - processes, file-systems, users

• support efficient context switching between processes, possibly supporting different per-process and per-user priorities

• impose limits and accounting of resource usage, per-process and per-user (e.g. varying scheduling timequantum, maximum execution time, maximum number of processes, maximum amount of memory, maximum open files)

• support constrained and exclusive access to resources (e.g. read-only, read-write access)

• permit sharing of resources when requested (shared access to memory, use of dynamically loaded libraries)

• permit requests to obtain, increase, or relinquish resource ownership