Multiprocessor Systems

Multiprocessor systems are the CPUs having more than one processor communicating each other and sharing same resources. Today is the world of multiprocessor systems which is also called tightly coupled systems or parallel systems. All the processors usually share bus, cache and memory. Modern multiprocessor systems have both local separate L1 cache and shared L2 cache.

Multiprocessor systems can give improved performance. If the number of processor is N, then the total output of entire system should be N times the output of individual, at least theoretically. This is not practical because of the overhead associated with maintaining and controlling different processors and contention of shared resources.

Another advantage of multiprocessor systems are that it economical than multiple single processor systems because of the cost associated with peripherals storage and power supplies. On the other hand multiprocessor systems can share these resources.

Reliability associated with each system also increases in multiprocessor systems. This is because a properly configured multiprocessor system has the ability withstand any damage caused to any of the individual processor in it.

Timesharing or Multitasking systems

Timesharing or Multitasking systems are a enhancement over multiprogramming systems to enable more than one user to share the resources of one system simultaneously. All users simultaneously interact with a single system through different clients giving impression to each user that he is using the resources of entire system own his own. But actually different  time slots are alloted to each user separately and so small that user is unaware of that fact.

Each user has at least one program to be executed residing in memory. This is called a process. Thus in a time sharing or multitasking system, each process is executed only for a very small time , that is until it finishes or waits for an I/O. Then CPU  transfers control to next user. Time sharing system more complex than multitasking system.