Operating System

Operating System Process Management





In operating systems, process is defined as “A program in execution” [10]. Process can be considered as an entity that consists of a number of elements, including: identifier, state, priority, program counter, memory pointer, context data, and I/O request. The above information about a process is usually stored in a data structure, typically called process block. Figure 1 shows a simplified process block [10]. Because process management involves scheduling (CPU scheduling, I/O scheduling, and so on), state switching, and resource management, process block is one of the most commonly accessed data type in operating system. Its design directly affects the efficiency of the operating system. As a result, in most operating systems, there is a data object that contains information about all the current active processes. It is called process controller. Figure 2 shows the structure of a process controller [10], which is implemented as a linked-list of process blocks.

A process is a program in executionl A process needs certain resources, including CPU time, memory, files, and I/O devices, to accomplish its taskn The operating system is responsible for the following activities in connection with process managementl Process creation and deletionl Process suspension and resumptionl Provision of mechanisms for:4process synchronization4process communication







Main Memory Management



Memory is a large array of words or bytes, each with its own addressl It is a repository of quickly accessible data shared by the CPU and I/O devicesMain memory is a volatile storage device. It loses its contents in the case of system failureThe operating system is responsible for the following activities in connections with memory managementl Keep track of which parts of memory are currently being used and by whoml Decide which processes to load when memory space becomes availablel Allocate and deallocate memory space as needed







file management system



a computer program that provides a user interface to work with file systems. The most common operations used are create, open, edit, view, print, play, rename, move, copy, delete, attributes, properties, search/find, and permissions. Files are typically displayed in a hierarchy. Some file managers contain features inspired by web browsers, including forward and back navigational buttons.





























I/O System Management

he I/O system consists of:l A buffer-caching system l A general device-driver interfacel Drivers for specific hardware devices

Secondary Storage Management

Secondary storage management is a classical feature of database management systems. It is usually supported through a set of mechanisms. These include index management, data clustering, data buffering, access path selection and query optimization.
None of these is visible to the user: they are simply performance features. However, they are so critical in terms of performance that their absence will keep the system from performing some tasks (simply because they take too much time). The important point is that they be invisible. The application programmer should not have to write code to maintain indices, to allocate disk storage, or to move data between disk and main memory. Thus, there should be a clear independence between the logical and the physical level of the system.

Since main memory (primary storage) is volatile and too small to accommodate all data and programs permanently, the computer system must provide secondary storage to back up main memoryMost modern computer systems use disks as the principle on-line storage medium, for both programs and dataThe operating system is responsible for the following activities in connection with disk management: l Free space managementl Storage allocationl Disk scheduling

Protection System

An active protection system, or APS, protects a tank or other armoured fighting vehicle from incoming fire before it hits the vehicle's armour. There are two general categories: soft kill systems, which use jamming or decoys to confuse a missile's guidance system, and hard kill systems, which attempt to detect and destroy incoming projectiles.

Protection refers to a mechanism for controlling access by programs, processes, or users to both system and user resourcesThe protection mechanism must: l distinguish between authorized and unauthorized usagel specify the controls to be imposedl provide a means of enforcement

Command interpreter system

A command interpreter is the part of a computer operating system that understands and executes commands that are entered interactively by a human being or from a program. In some operating systems, the command interpreter is called the shell.

Many commands are given to the operating system by control statements which deal with:l Process creation and managementl I/O handlingl Secondary-storage managementl Main-memory managementl File-system access l Protection l Networking