main()

{

fork();

 

printf(“Hello World!”);

}

Output for the above unix program is

• Responsiveness


• Resources sharing


• Economy


• Utilization of multiprocessor architectures.

In a multiprocessor system there exist several caches each may containing a copy of same variable A. Then a change in one cache should immediately be reflected in all other caches this process of maintaining the same value of a data in all the caches s called cache-coherency.

Scheduler deals with the problem of deciding which of the process in the ready queue is to be allocated the CPU. Short Term Schedulers, Long Term Schedulers

Micro-kernal : A micro-kernel is a minimal operating system that performs only the essential functions of an operating system. All other operating system functions are performed by system processes.

Monolithic : A monolithic operating system is one where all operating system code is in a single executable image and all operating system code runs in system mode.

When a process requests an available resource, system must decide if immediate allocation leaves the system in a safe state. System is in safe state if there exists a safe sequence of all processes. Deadlock Avoidance : ensure that a system will never enter an unsafe state.

An interpreter reads one instruction at a time and carries out the actions implied by that instruction. It does not perform any translation. But a compiler translates the entire instructions.

Mutual exclusion

Hold and wait

No preemption

Circular wait

Data registers - can be assigned to a variety of functions by the programmer. They can be used with any machine instruction that performs operations on data.
Address registers - contain main memory addresses of data and instructions or they contain a portion of the address that is used in the calculation of the complete addresses.