4.1.5 Multiprogramming and Time Sharing System 4.1.6 Explain Deadlock

4.1.5 Identify between multiprogramming and time-sharing.

MULTIPROGRAMMING VS TIME SHARING SYSTEM

          Multiprogramming is the allocation of more than one concurrent program on a computer system and its resources. Multiprogramming allows using the CPU effectively by allowing various users to use the CPU and I/O devices effectively.
     
          Multiprogramming make sure thatthe CPU always has something to execute, thus increases the CPU utilization. On the other hand, Time sharing of computing resources among svereal users at the same time. Since this will allow a large number of users to work at a single computer system at the same time, it would lower the cost of providing computing capabilities.

MULTIPROGRAMMING

Multiprogrammin is the fast switching of CPU between several programs. A program is generally made up of several tasks. A tasks usually ends with some request to move data which would require some I/O operations to be execute.

TIME SHARING

          Time sharing, which was introduced in 1960s, is the sharing of computingresources among several users at the same time. In time sharing system, several terminals are attached to a single dedicated server having its own CPU.

          Actions/commands executed by the operating system of a time sharing system have a very short time span. Therefore the CPU is assigned to users at the terminals for a short time period,thus a user in a terminal gets the feeling that she has a CPU dedicated to her behind the terminal.

DIFFERENCE BETWEEN MULTIPROGRAMMING AND TIME SHARING SYSTEM

Main difference between multiprogramming and time sharing is the effective utilization of CPU time, by allowing several program to use the CPU at the same time but time sharing of a computing facility by several users that want to use the same faacility at the same time. Each user on a time sharing system get their own terminal and gets the feeling that they is using the CPU alone.

4.1.6 Explain Deadlock.

          A deadlock is a situation in which two computer programs sharing the same resource are effectively preventing each other from accessing the resource, resulting in both programs ceasing to function.The earliest computer operating systems ran only one program at a time. All of the resources of the system were available to this one program.
     
         Later, operating systems ran multiple programs at once, interleaving them. Programs were required to specify in advance what resources they needed so that they could avoid conflicts with other programs running at the same time. Eventually some operating systems offered dynamic allocation of resources. Programs could request further allocations of resources after they had begun running. This led to the problem of the deadlock. Here is the simplest example:

Program 1 requests resource A and receives it. Program 2 requests resource B and receives it. Program 1 requests resource B and is queued up, pending the release of B. Program 2 requests resource A and is queued up, pending the release of A.

Now neither program can proceed until the other program releases a resource. The operating system cannot know what action to take. At this point the only alternative is to abort (stop) one of the programs.
Learning to deal with deadlocks had a major impact on the development of operating systems and the structure of databases. Data was structured and the order of requests was constrained in order to avoid creating deadlocks.