A process is a program in execution. It is a unit of work within the system. Program is a passive entity , process is an active entity . Process needs resources to accomplish its task CPU, memory, I/O, files Initialization data Process termination requires reclaim of any reusable resources Single-threaded process has one program counter specifying location of next instruction to execute Process executes instructions sequentially, one at a time, until completion Multi-threaded process has one program counter per thread Typically system has many processes, some user, some operating system running concurrently on one or more CPUs Concurrency by multiplexing the CPUs among the processes / threads
1.36 Silberschatz, Galvin and Gagne ©2018, revised by S. Weiss 2020 Operating System Concepts – 10 th Edition Process Management Activities Creating and deleting both user and system processes Suspending and resuming processes Providing mechanisms for process synchronization Providing mechanisms for process communication Providing mechanisms for deadlock handling The operating system is responsible for the following activities in connection with process management:
1.37 Silberschatz, Galvin and Gagne ©2018, revised by S. Weiss 2020 Operating System Concepts – 10 th Edition Memory Management To execute a program all (or part) of the instructions must be in memory All (or part) of the data that is needed by the program must be in memory Memory management determines what is in memory and when Optimizing CPU utilization and computer response to users Memory management activities Keeping track of which parts of memory are currently being used and by whom Deciding which processes (or parts thereof) and data to move into and out of memory Allocating and deallocating memory space as needed
1.38 Silberschatz, Galvin and Gagne ©2018, revised by S. Weiss 2020 Operating System Concepts – 10 th Edition File-system Management OS provides uniform, logical view of information storage Abstracts physical properties to logical storage unit - file Each medium is controlled by device (i.e., disk drive, tape drive) Varying properties include access speed, capacity, data- transfer rate, access method (sequential or random) File-System management Files usually organized into directories Access control on most systems to determine who can access what OS activities include Creating and deleting files and directories Primitives to manipulate files and directories Mapping files onto secondary storage Backup files onto stable (non-volatile) storage media
1.39 Silberschatz, Galvin and Gagne ©2018, revised by S. Weiss 2020 Operating System Concepts – 10 th Edition Mass-Storage Management Usually disks used to store data that does not fit in main memory or data that must be kept for a “long” period of time Proper management is of central importance Entire speed of computer operation hinges on disk subsystem and its algorithms OS activities Mounting and unmounting Free-space management Storage allocation Disk scheduling Partitioning Protection
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- Gagne, Galvin