The UNIX operating system for a multiprocessor system has a number of extra features as compared to normal UNIX operating system. Let's first consider the design objectives of multiprocessor UNIX. The original UNIX created by Dennis Ritchie and Brian Kernighan was created as general purpose, portable, time-sharing uniprocessor operating system.
The OS functions comprising virtual memory management, processor scheduling, I/O devices etc are applied with a huge amount of system software. Generally size of OS is larger than size of main memory. The part of OS which exist in main memory is known as kernel. For a multiprocessor OS is created on 3 models viz: Floating executive model, Master slave model, multithreaded kernel. These UNIX kernels are applied with monitors and locks semaphores.