1. SIMULATOR

Simulation work to analyze its various operating policies and designs. Main aim is to emphasize the usefulness and importance of simulation in support of operating system. Simulation can be applied in many critical areas and enables one to address various issues. Here simulation provides insights into the design of operating system.

Simulation is used to decide which policy of page-replacement is best that makes the tasks of memory management in operating system efficient in spite of the constraint of limited physical memory.

POLICIES:

Designers of an operating system are required to zero-in on one of several alternate policies that will be adopted for replacement /swapping of memory pages. Moreover, this decision need to be taken before actually implementing the policy in operating system.

BENEFITS OF O.S.

 An operating system is an important part of almost every computer system. A major goal of an operating system is to hide all the complexities and give the programmer a more convenient set of instructions to work with. Operating system is responsible for managing the resources and providing convenience to the user. Among all memory management is one of the most important function of the operating system.

Computer memory is organized into at least two levels, referred to as main memory and secondary memory. The part of the operating system that manages the memory hierarchy is called the memory manager.

Its job is to keep track of which part of memory are in use and which are not, to allocate memory to processes when they need it and de-allocate when they are done and to manage swapping between main memory and disk when main memory is too small to hold all the processes.

The real memory management systems require the entire process image in the main memory at the time of execution. The Virtual memory system, which is the base of present research work, removes this restriction.

At any time only the portion of process that is currently needed, is loaded into the main memory, while keeping the other parts on the disk. The virtual memory systems can be implemented using paging, segmentation and combined scheme.

 Because of this technique, the user programs are free from the size of physical memory available. The user program can be of large size than the main memory. As the entire program is not needed in the main memory, program can be executed in parts(Stallings,2004)

GOOD PAGE:

A good page replacement takes into account the idea that whenever a page is needed, the probability of finding that page in memory is sufficiently high. The chosen policy should perform better than others during actual operations of the system.

This paper reports the design of a simulator for performance evaluation of alternate page-replacement policies in memory management module of a general purpose operating system.