Multi Programming and Time Sharing Security

Sunday, December 5, 2010

Deadlocks is one example that you may encounter in time sharing and multiprogramming. Deadlock is a situation where in two or more competing actions are each waiting for the other to finish, and thus neither ever does. Client applications using the database may require exclusive access to a table, and in order to gain exclusive access they ask for a lock. If one client application holds a lock on a table and attempts to obtain the lock on a second table that is already held by a second client application, this may lead to deadlock if the second application then attempts to obtain the lock that is held by the first application. Often, neither avoidance nor deadlock prevention may be used.
Instead deadlock detection and process restart are used by employing an algorithm that tracks resource allocation and process states, and rolls back and restarts one or more of the processes in order to remove the deadlock. Detecting a deadlock that has already occurred is easily possible since the resources that each process has locked and/or currently requested are known to the resource scheduler or OS.

Resource allocation another problem that you may encountered in the time sharing and multiprogramming environment. Resource allocation is used to assign the available resources in an economic way. It is part of resource management. In project management, resource allocation is the scheduling of activities and the resources required by those activities while taking into consideration both the resource availability and the project time.
Modern operating systems often provide users and applications with a virtual machine, an interface to the underlying hardware that makes it appear as though the user is the only user of the machine and it's hardware. With a single simple constraint, it determines the allocation of a fixed amount of resources to a given number of activities in order to achieve the most effective results. It may be viewed as a special case of the nonlinear programming or nonlinear integer programming problem.
We cannot ensure the same security between time-shared machine and dedicated machine. Because if we consider time-shared machine many user can access the files unlike the dedicate machine that only has one primary function or task like automobile might have an onboard computer that is dedicated solely to navigation. Also in time-shared machine a multitude of external users serving each rapidly and simultaneously and process many data.