This chapter introduces the concept of the operating system (OS) as found in computers. At the end of this chapter; the reader should be able to understand what am operating system is, it's relationship with Computer resources and users, it's components and functions and it's operating system and understand the most commonly used OS terminologies. This particular episode includes some brief knowledge on WINDOWS, UNIX and LINUS.
DEFINITION: WHAT IS AN OPERATING SYSTEM (OS)?
An operating system ( or OS usually called in the IT world) is an integrated set of control programs designed to manage Computer resources and maximize the overral operations and effectiveness of the computer system. To put it in the simplest of terms, it is the 'executive resources managers', the part of the computer system that manages all of the hardware and all of the software. It controls who can use the system and how? In a nutshell, it is usually called the BOSS. Therefore, when the users sends a command, the OS must make sure that the command is executed and, if not executed, must arrange for the user to get a message explaining the error. Even though it is not the operating system thy executes the command of sends the error message, it does control the parts of the system that performs such task.
OPERATING SYSTEMS AS A MANAGER OF RESOURCES
WHAT ARE RESOURCES? Resources are things that cost money. Operating system are primarily resources managers. The main resources they manage includes Processors, Storage, Input/Output devices, communication devices, Files and data.
Operating system performs many functions such as:
• implementing the user interface,
• sharing hardware among users,
• allowing users to share data among themselves,
• preventing users from interfering with one another
• scheduling resources among users,
• facilitating input/Output
• recovering from errors,
• accounting for resources usage,
• facilitating parallel operations,
• organizing data for secure and rapid access,
• and handling network communication.
Examples of operating systems include:
• Disk Operating System (DOS) for single - User, computer
• Windows Operating System for Single - User, and multi-user computers.
• Unix Operating System for multi - user computer systems
• Network Operating systems.
COMPONENTS OF OPERATING SYSTEMS
There are basically four major components of an operating system. They include; Memory Managers (MM), Processor Managers (PM), Device Managers (DM), and File Managers (FM).
√ Memory Managers and it's Functions
The Memory Managers is in charge of main memory. The basic Functions are:
• To keep track memory. What parts are in use and by whom? What parts of memory are FREE(Not in use)
• If in a multiprogramming environment, decides which process gets memory, when it gets it, and how much. It sets up a table to keep track of who is using each section of memory.
• To allocate Memory when the process request it, based on the allocation Policy
• To reclaim memory when a process no longer needs it or the process has been terminated
√ Processor Managers and it's Functions
The Processor Managers (PM) decides how to allocate Central Processing Unit (CPU). The main Functions are:
• To keep track of processors and the status of process ( a process is defined as an instance of execution of a program). The program that does this is sometimes referred to as TRAFFIC CONTROLLER.
• To decide who will have the chance to use the processor. The program that does this is the JOB SCHEDULER. It chooses from the jobs submitted to the system and decides which one will be allowed into the system. In multiprogramming environment this is also called PROCESSOR SCHEDULER and it decides which process gets the processor, when and how much.
• To allocate Processor to a PROCESS by setting up necessary hardware/software registers and tables.
• To reclaim processor when a process relinquishes processor usage, terminates, or reaches allowed amount of usage.
Conceptually, the Processor Manager has two levels of responsibilities: to handle jobs as they Enter the system, and to manage each of the process within those jobs.
√ Device Manager and it's Functions
The main function of the Device Manager are:
• To keep track of devices, channel and control units. It does this by monitoring each of these devices. The program module that does this is called the I/O TRAFFIC CONTROLLER.
• To decide who should be allocated a device. If devices have to be shared, to decide who gets what and how much to get. The program that does this is called SCHEDULER.
• To choose the most efficient way to allocate all of the systems device such as printers, terminals, disk drives etc, based on a scheduling policy.
• To reclaim devices. These days however, I/O is made to terminate automatically.
√ Information Manager (File Manager) and it's Functions
The Information Managers, sometimes called the File Manager, basically performs the following functions:
• Keeps tracks of information, it's location, use status, etc. These facilities are collectively called FILE SYSTEM and they may include data files, assemblers, compilers, and Application programs.
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| File Manager |
• Decides who makes use of information, enforces protection requirements and provides necessary accessing routines and access policies, such as System only, user group only, Group only, or General access. It also controls the amount of flexibility each user is allowed with a particular File such as Read/Write Only, or the authority to create and/or delete records.
• Allocates information, e.g. Open a file
• De - Allocates Information e.g. Close a file