Swapping Ready Queue may be empty all the processes may be in the I/O queues – Swap processes from the I/O queues to an on disk Intermediate swap space, i.e., raw disk partition with no file system (faster swapping) – OS selects a process from the to place in the Ready Queue Intermediate Queue swap space, i.e., raw disk partition with no file system (faster swapping) – Partitioning Fixed Size Equal Size Unequal Size Variable Size Addresses Logical Address location relative to the beginning of the program (location zero) program instructions contain logical addresses Physical Address actual location in main memory base address physical address of the current starting location of process in physical memory processor adds the base address to the logical address to obtain the physical address Paging pages small fixed size chunks of program – frames small fixed size chunks of memory – No external fragmentation of memory Internal fragmentation ½ of last frame Page tables maintain list of frames in use OS also a list of free frames Demand Paging Each page of a process is allocated a frame in memory only when it is referenced from a previous frame Page Fault Page Replacement Algorithms Trashing repeatedly throwing out pages just before they were to be referenced Real Memory actual physical memory
Swapping Ready Queue may be empty – all the processes may be in the I/O queues Swap processes from the I/O queues to an Intermediate on disk swap space, i.e., raw disk – partition with no file system (faster swapping) OS selects a process from the Intermediate Queue to place in the Ready Queue swap space, i.e., raw disk – partition with no file system (faster swapping) Partitioning Fixed Size Equal Size Unequal Size Variable Size Addresses Logical Address location relative to the beginning of the program (location zero) program instructions contain logical addresses Physical Address actual location in main memory base address physical address of the current starting location of process in physical memory processor adds the base address to the logical address to obtain the physical address Paging pages – small fixed size chunks of program frames – small fixed size chunks of memory No external fragmentation of memory Internal fragmentation ½ of last frame Page tables maintain list of frames in use OS also a list of free frames Demand Paging Each page of a process is allocated a frame in memory only when it is referenced from a previous frame Page Fault Page Replacement Algorithms Trashing repeatedly throwing out pages just before they were to be referenced Real Memory actual physical memory
Operating%20Systems.docx