CSE NOTES

Demand paging -Loading the entire program in the physical memory at program execution time is not so good because the user does not need the entire program in memory at a time. -An alternative strategy is to load pages only as they are need this technique is known as demand paging. -With demand paging virtual memory, pages are only loaded when they are demanded during program execution pages that are never accessed thus never loaded into physical memory.    -A demand paging system is a similar to paging system with swapping, -But here it uses a lazy swap where it never swap a pages into memory unless that page will be need. -In demand paging pager is more suitable than swap er. 

Paging -Paging is storage mechanism that allows operating system to retrieve a process from the secondary memory into the main memory in the form of pages. -In the paging method the memory is divided  into small fixed size block of the physical memory that is called frame. -The size of the frame should be kept the same as that of pages to have maximum utilization of the main memory and to avoid external fragmentation. -Paging is use for the faster access to the data and it is a logical concept. 

swapping -A process can be swapped temporary out of memory to a backing store and then brought back into memory for continued execution. -Switching a process from the main memory to backing store is called swap out and switching a process from disk to the main memory is called swap in. -The swap out and swap in to process is called as swapping. -swapping is increase the context of switch.   Benefits of swapping: -It offer a higher degree of multi programming. -It allows a dynamic relocation. -It is help to get better utilization of the main memory.                     

memory allocation techniques memory allocation techniques is two types :                                                                         1. continuous memory allocation                                                                        2.non-continuous memory allocation Continuous memory allocation: -In this memory allocation all available memory space remain together. It means freely available memory partition are not scatter here.Their across the whole memory space. -when any user process request for the memory a single section of the continuous memory block is given to the process according to its need.we can achieve the continuous memory allocation by dividing memory into the fixed sized. -A single process is allocated into the fixed sized single partition but this will increase the degree of the multi programming means move than one process in the main memory that bounds the number of fixed partition done in memory international fragmentation increase b

Scheduler  -Scheduler is the special system software which handle the process scheduling in various ways. Their the main tasks is to select the jobs to be submitted into the system and to decide with process to run. -There are three types of scheduler:                                                         1.long term scheduler                                                         2.medium term scheduler                                                         3.short term scheduler  Long term scheduler: -It is also known as job scheduler. The function of the long term scheduler is to select the job from the pull of the jobs and loaded the jobs in the main memory called ready queue of the computer. So long term scheduler is known as job scheduler. -Ready queue is a data structure in which the data is entered in the queue first will be entire ed so it is a FIFO structure. -Queue has a two ends first one is rear and second one is front. -The jobs are loaded into t