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Operating Systems Advanced OS – B OS Advanced Memory & Processor Management OS Advanced Memory Management OS Advanced Memory management is concerned with managing the computer’s available pool of memory, allocating space to application routines and making sure they do not interfere with each other OS Advanced Because of the speed differences between memory and other hardware, the OS spends more time waiting for Input/Output than processing data OS Advanced Generally the more programs in memory, the greater the utilization of the CPU OS Advanced A single processor cannot execute two or more programs simultaneously (“at the same time”) OS Advanced A single processor can execute two or more programs concurrently (“over the same time period”) OS Advanced There are two ways of managing multiple concurrent programs Fixed-Partition Memory Management & Dynamic Memory Management OS Advanced Fixed-Partition Memory Management Dividing the available memory into fixed size partitions which will hold programs when they are loaded OS Advanced Fixed partitions are loaded upon system startup, and if not sufficient for the largest program to be loaded wastes space and is inefficient. However it is simple to do. OS Advanced Dynamic management allocates a large pool of memory and makes it available for programs as they are loaded into memory OS Advanced When the program is loaded just enough memory is allocated to fit the size of the program from the larger memory pool OS Advanced Dynamic memory management wastes little space, but is harder to do OS Advanced One problem with Dynamic memory management is Fragmentation OS Advanced To keep two or more programs from interfering with each other the OS memory protection routine intercepts the problem and terminates the offending application OS Advanced Virtual Memory Virtual = “not in actual fact” Memory that acts like real memory but is not real memory OS Advanced Real Memory – Physical memory chips Virtual Memory – Logical memory chips OS Advanced Total memory is divided into the Real Memory & Logical Memory Total Memory = Physical Amount + Virtual Memory. Allocated on another disk (usually the HD) OS Advanced Programs are swapped to and from virtual memory into physical memory as needed by the current processes OS Advanced This swapping process is transparent to the user and done in the background by the OS OS Advanced Page Faults How programs are swapped into physical memory When a process points to a virtual memory address a page fault is recognized by the OS… OS Advanced Then the required swap-in occurs and the operation can begin OS Advanced When a system spends to much time swapping from virtual to physical memory we have Thrashing which degrades system performance OS Advanced Processor Management OS Advanced Time-Slicing is the approached used on most modern computers to handle concurrent program execution OS Advanced Program 1 gets 0.001 secs to function, then Program 2 gets 0.001 secs to function, time-slice depends on OS OS Advanced A program uses its time-slice until one of two things happen: It requests an I/O function (wait state) or It uses up its time-slice End 02-04-05 OS Advanced Scheduling & Queuing Processor management is concerned with internal priorities of programs already in memory OS Advanced Determining which program runs next is determined by the Queuing Routine and a Scheduler OS Advanced Queuing Routine As programs enter into memory they are placed in a queue OS Advanced There are internal and external priorities OS Advanced External priorities are concerned with loading the program into memory in the first place OS Advanced Internal priorities are concerned with which program goes next in the queue OS Advanced By this queuing and scheduling system the applications we use can be time-sliced and we are assured that they will function OS Advanced Spooling Freeing up memory when performing jobs like printing. Data is spooled to a HD and then sent to a printer when the CPU or printer is idle. This frees up Memory and CPU cycles for other tasks OS Advanced Deadlock The result of poor resource management. Happens when two processes require the same resource, either physical or logical (memory) OS Advanced Memory & Processor Management is a key function of an OS, it determines how useful the OS is. OS Advanced Questions?