lec9_memorymgt0

Lec9_memorymgt0 - Lecture 9 Memory Management Memory action definitions Swapping When program size exceeds main memory processes are moved out of

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Lecture 9: Memory Management Memory action definitions: Swapping – When program size exceeds main memory, processes are moved out of memory to secondary storage device. However, there can be large context switch overhead when accessing processes in the secondary storage device. Schedulers can use it only when the task execution time is very large compared to this context switch overhead. Extremely slow method of CPU access to memory. Overlaying – When program size exceeds main memory, new code and data are brought into memory replacing old code and data. Obviously, there is much opportunity for data loss and memory corruption . Because of the large access times involved with storage disk access, it’s also very inefficient for real-time purposes. The process of overlaying memory in main memory is analogous to thrashing of the cache. Partitioning – Memory is separated into fixed sized contiguous blocks avoiding the need for swapping. Tasks reside in contiguous partitions, but memory usage is inefficient and can be fragmented. It is useful when the number and size of tasks is well-known and fixed. Fragmentation results when task memory is broken up in RAM when partitions become too small for the tasks that are allocated to them. Paging – Fixed size blocks are stored for program segments in non-contiguous memory. Dynamic allocation of memory is slow due to the capacitor charging/discharging, and is unusable with real-time systems due to the large source of real-time uncertainty, especially in hard real-time applications. Page
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This note was uploaded on 04/07/2010 for the course ELEC ecse 421 taught by Professor Guss during the Winter '10 term at McGill.

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Lec9_memorymgt0 - Lecture 9 Memory Management Memory action definitions Swapping When program size exceeds main memory processes are moved out of

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