Q. What is multi-threaded unix kernel?

Multi-threaded UNIX kernel: We know threads are light-weight processors demanding minimal state information comprising the processor state and contents of relevant registers. A thread being a process is capable of executing by itself. In a multiprocessor system, more than one processors may execute simultaneously with each processor possibly executing more than one threads, with the restriction that those threads which share resources must be allotted to one processor. But the threads that do not share resources may be allotted to different processors. In this model in order to differentiate many threads demanding different sets of kernel resources spin locks or semaphores are used.