Q1. Explain System Model.
Ans. A system model consists of many resources, which are shared or distributed among several competing processes. Memory, CPU, disk space, printers and tapes are the example of resources. When a system has two CPUs then we can say that there are two instances of CPUs. Similarly, in a network, we may have ten printers and we can say that there are ten instances of printers.
In such situations, we are not bothered about which instance of the requested resources in processing the request. When a process is executing, it requests for a resources before using it and it must release the resource after using it. Any process carries out the assigned task. It cannot make more requests than the maximum number available in the system.
A process uses the request in the following sequence.
- Request process request for necessary resources. If the resources are not free then the process has to wait until the resources are free so that it can acquire control on the resources.
- Use process can operate/use the acquire resource to carry out assigned task.
- Release process releases the resources when operation is complete on the acquired resource.
Following are the three major operations which are processed on a resource:
Figure: General Pattern for resource allocation