Operating System-Memory Management
Download as PPTX, PDF26 likes15,751 views
The document discusses memory management techniques in operating systems, focusing on paging, segmentation, fragmentation, virtual memory, page tables, and swapping. Paging ensures data accessibility by loading pages into main memory, while segmentation divides memory into logical segments to reduce fragmentation. Fragmentation occurs when files are stored in non-contiguous clusters, slowing down access, and swapping allows processes to be temporarily moved from main memory to secondary storage for efficient execution.
Operating System-Memory Management
- 1. A GLANCE ON MEMORY MANAGEMENT SECTION OPERATING SYSTEM akmalcikmat
- 2. Paging A technique used by virtual memory OS to help ensure that the data we need is available as quickly as possible. The operating system copies a certain number of pages from storage device to main memory. When a program needs a page that is not in main memory, the operating system copies the required page into the memory and copies another page back to the disk. akmalcikmat
- 3. Cont. One says that the operating system pages the data. Each time a page is needed that is not currently in memory, a page fault occurs. An invalid page fault occurs when the address of the page being requested is invalid. In this case, the application is usually aborted akmalcikmat
- 4. Segmentation Segmentation is a technique to break memory into logical pieces where each piece represents a group of related information. For example ,data segments or code segment for each process, data segment for operating system and so on. Segmentation can be implemented using or without using paging. Unlike paging, segment are having varying sizes and thus eliminates internal fragmentation. External fragmentation still exists but to lesser extent. akmalcikmat
- 5. akmalcikmat
- 6. Fragmentation Refers to the condition of a disk in which files are divided into pieces scattered around the disk. Fragmentation occurs naturally when one use a disk frequently, creating, deleting, and modifying files. At some point, the operating system needs to store parts of a file in non-contiguous clusters. This is entirely invisible to users, but it can slow down the speed at which data is accessed because the disk drive must search through different parts of the disk to put together a single file. akmalcikmat
- 7. Cont. Fragmentation can also refer to RAM that has small, unused holes scattered throughout it. This is called external fragmentation. With modern OS that use a paging scheme, a more common type of RAM fragmentation is internal fragmentation. This occurs when memory is allocated in frames and the frame size is larger than the amount of memory requested akmalcikmat
- 8. akmalcikmat
- 9. Virtual Memory An imaginary memory area supported by some OSs (for example, Windows but not DOS) in conjunction with the hardware. One can think of virtual memory as an alternate set of memory addresses. Programs use these virtual addresses rather than real addresses to store instructions and data. When the program is actually executed, the virtual addresses are converted into real memory addresses. akmalcikmat
- 10. akmalcikmat
- 11. akmalcikmat
- 12. Page Table A page table is the data structure used by a virtual memory system in a computer OS to store the mapping between virtual addresses and physical addresses. Virtual addresses are used by the accessing process, while physical addresses are used by the hardware or more specifically to the RAM. Each mapping is also known as a page table entry (PTE) akmalcikmat
- 13. akmalcikmat
- 14. Swapping Swapping is a mechanism in which a process can be swapped temporarily out of main memory to a backing store, and then brought back into memory for continued execution. Backing store is a usually a hard disk drive or any other secondary storage which fast in access and large enough to accommodate copies of all memory images for all users. It must be capable of providing direct access to these memory images akmalcikmat