Process Management

A program running on a computer, whether visible to the user or not, is commonly referred to as a process. Process management refers to the facilities provided by the OS to support the creation, execution, and destruction of processes.

Creating a process involves allocating memory space for the process, loading the program's executable code into memory, telling the scheduler to run the program, and other tasks specific to the operating system.


The scheduler is the portion of the operating system that causes the program to be executed on the CPU, that is, 'scheduled' for execution. If the scheduler supports preemptive multitasking, it can change the program currently executing on the CPU to that of another program when it determines that the first program has executed for a predetermined amount of time. The amount of time allocated to a given process may depend on the needs of the process in question and the user's priority level for that process.


Destroying a process involves releasing any resources (including dynamically allocated memory, file references, and I/O ports) held by the program and ensuring that a different program is scheduled for execution.


Depending on the operating system, process management can be more simple or more complex than treated above. Several examples will illustrate:


The operating systems originally deployed on mainframes, and, much later, the original microcomputer operating systems, only supported one program at a time, requiring only a very basic scheduler. Each program was in complete control of the machine while it was running.


Multitasking (timesharing) first came to mainframes in the 1960's and to microcomputers in the mid-1980's, although, in both cases, for the most part, it wasn't until years later that the capability was perfected and made widely available.


Classic Mac OS generally supported only cooperative multitasking, Application programs running with classic Mac OS must yield CPU time to the scheduler by calling a special function for that purpose.


Classic AmigaOS did not properly track resources allocated by processes at runtime. If a process had to be terminated, the resources would be lost to programs run in the future, until the machine was restarted.

Please follow these links for details on other tasks performed by Operating System:
Memory Management
Process Management
Disk and File Management
Networking
Security
Graphical User Interface
Device Driver Management