CSE NOTES

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

Process control block -Each process is represented in the operating system by the process control block also called as task control block. -It contains many pieces of information associated with a specific process include these Process states: The state may be new/ready,running,waiting,haltered and soon. Program counter: The counter can be indicate to the address of the next instruction to be executed for this process. CPU registers: The register vary in number and type depending in the computer or architecture .they includes the accumulator,index register,stack pointer , general purpose of register. Memory management information: It may be includes such information as the value of the base and limit register, the page tables or segment tables depending on the memory system used by the operating system. Accounting information: It includes the account of the CPU and real time used,time limits account number,job or process number and soon. I/O status inf

-Process state means current activity of process. -When process is execute it changes the state generally state of process is determine by the current activity of process. -Each process may be in one of the following state. new- the process is being is oriented. ready- the process is waiting to be assigned to the processor. waiting - the process is waiting for some event (I/O operation) to occur. running - the process is being executed.  terminated -the process as finished the execution. process state diagram: -The pictorial is represented to the process changing from one process to another process during       there  execution is known as process state diagram. -A process can be change for one process in the following manner. new ready: The operating system(os) create a process and prepares the process to be executed ,then the os moved the process into the ready queue.  ready running: When it is time to select a process to run, the os selects one jo