tailieunhanh - Lecture Operating system concepts (Fifth edition): Module 8 - Avi Silberschatz, Peter Galvin

Module 8 - Memory management. After completing this unit, you should be able to: Explain the difference between logical and physical addresses, explain the difference between internal and external fragmentation, explain the following allocation algorithms. | Lecture Operating system concepts Fifth edition Module 8 - Avi Silberschatz Peter Galvin Module 8 Memory Management Background Logical versus Physical Address Space Swapping Contiguous Allocation Paging Segmentation Segmentation with Paging Silberschatz and Galvin 1999 Background Program must be brought into memory and placed within a process for it to be executed. Input queue collection of processes on the disk that are waiting to be brought into memory for execution. User programs go through several steps before being executed. Silberschatz and Galvin 1999 Binding of Instructions and Data to Memory Address binding of instructions and data to memory addresses can happen at three different stages. Compile time If memory location known a priori absolute code can be generated must recompile code if starting location changes. Load time Must generate relocatable code if memory location is not known at compile time. Execution time Binding delayed until run time if the process can be moved during its execution from one memory segment to another. Need hardware support for address maps . base and limit registers . Silberschatz and Galvin 1999 Dynamic Loading Routine is not loaded until it is called Better memory-space utilization unused routine is never loaded. Useful when large amounts of code are needed to handle infrequently occurring cases. No special support from the operating system is required implemented through program design. Silberschatz and Galvin 1999 Dynamic Linking Linking postponed until execution time. Small piece of code stub used to locate the appropriate memory- resident library routine. Stub replaces itself with the address of the routine and executes the routine. Operating system needed to check if routine is in processes memory address. Silberschatz and Galvin 1999 Overlays Keep in memory only those instructions and data that are needed at any given time. Needed when process is larger than amount of memory allocated to it. .