Lesson 6: Basics of Operating System

What is Operating System?

  • A computer’s operating system is a collection of programs that manage and coordinate the activities taking place within the computer and it is the most critical piece of software installed on the computer. The operating system boots the computer, launches application software, and ensures that all actions requested by a user are valid and processed in an orderly fashion
  • For example, when you issue the command for your computer to store a document on your hard drive, the operating system must perform the following steps:
  • make sure that the specified hard drive exists,
  • verify that there is adequate space on the hard drive to store the document and then store the document in that location, and
  • update the hard drive’s directory with the filename and disk location for that file so that the document can be retrieved again when needed.
  • In addition to managing all of the resources associated with your local computer, the operating system also facilitates connections to the Internet and other networks. In general, the operating system serves as an intermediary between the user and the computer, as well as between application programs and the computer system’s hardware. Without an operating system, no other program can run, and the computer cannot function. Many tasks performed by the operating system, however, go unnoticed by the user because the operating system works in the background much of the time.


Layers need to be concerned with layer below (and above)

Layers are isolated from certain changes

Functions of an Operating System

  • Operating systems have a wide range of functions— some of the most important are discussed next.
  • Interfacing with Users: one of the principal roles of every operating system is to translate user instructions into a form the computer can understand. It also translates any feedback from hardware—such as a signal that the printer has run out of paper or that a new hardware device has been connected to the computer—into a form that the user can understand.
  • The means by which an operating system or any other program interacts with the user is called the user interface; user interfaces can be text-based or graphics-based. Most, but not all, operating systems today use a graphical user interface (GUI).
  • Booting the Computer: the first task your operating system performs when you power up your computer is to boot the computer. During the boot process, the essential portion, or core, of the operating system (called the kernel) is loaded into memory. The kernel remains in memory the entire time the computer is on so that it is always available; other parts of the operating system are retrieved from the hard drive and loaded into memory when they are needed. Before the boot process ends, the operating system determines the hardware devices that are connected to the computer and configured properly, and it reads an opening batch of instructions.
  • Typically, many programs are running in the background all the time, even before the user launches any application software. Some of these programs are startup programs that are launched automatically by the operating system during the boot process; regardless of how programs are launched, they all consume memory and processing power.
  • Configuring Devices: the operating system also configures all devices connected to a computer. Small programs called device drivers (or simply drivers) are used to communicate with peripheral devices, such as monitors, printers, portable storage devices, and keyboards. Most operating systems today include the drivers needed for the most common peripheral devices. In addition, drivers often come on a CD packaged with the peripheral device or they can be downloaded from the manufacturer’s Website
  • Managing Network Connections: the operating system is also in charge of managing your network connections, such as a wired connection to a home or office network or wireless connections at home, school, work, or on the go. For instance, as you move into range of a wireless network, the operating system will notify you that a new wireless network is available and then either connect your device to that network or wait for your instruction to connect to the network, depending on your device’s wireless network settings.
  • Managing and Monitoring Resources and Jobs: as you work on your computer, the operating system continuously manages your computer’s resources (such as software, disk space, and memory) and makes them available to devices and programs when they are needed. If a problem occurs—such as a program stops functioning or too many programs are opened for the amount of memory installed in the computer—the operating system notifies the user and tries to correct the problem, often by closing the offending program.
  • File Management: another important task that the operating system performs is file management—keeping track of the files stored on a computer so that they can be retrieved when needed. You can organize the files on a storage medium into folders to simplify file management. Usually the operating system files are stored inside one folder (such as a Windows folder), and each application program is stored in its own separate folder inside a main programs folder (such as Program Files).
  • Other folders designed for storing data files are typically created by the operating system for each user (such as My Documents, My Music, and My Pictures folders); individuals may create additional folders, as desired, to keep their files organized. Folders can contain both files and other folders (called subfolders).
  • Files and folders are usually viewed in a hierarchical format; the top of the hierarchy for any storage medium is called the root directory (such as C: for the root directory of the hard drive C). The root directory typically contains both files and folders. To access a file, you generally navigate to the folder containing that file by opening the appropriate drive, folder, and subfolders. Alternatively, you can specify the path to a file’s exact location.
  • For example, the path C:\ My Documents\ Letters\ Mary
  • leads through the root directory of the C drive and the My Documents and Letters folders to a file named Mary. Similar paths can also be used to access the various files on a computer. You specify a filename for each file when you initially save the file on a storage medium; there can be only one file with the exact same filename in any particular folder on a storage medium.
  • Filenames typically include a file extension (usually three or four characters preceded by a period) at the end of the filename, which indicates the type of file. File extensions are automatically added to a filename by the program in which that file was created. File extensions should not be changed by the user because the operating system uses them to identify the program that should be used to open the file.
  • For instance, if you issue a command to open a file named Letter to Mom.docx, the file will open using the Microsoft Word program because the .docx file extension is associated with the Microsoft Word program. Files can be opened, as well as moved, copied, renamed, and deleted, using a file management program such as File Explorer.
  • Security: a computer’s operating system can use passwords, biometric characteristics (such as fingerprints), and other security procedures to limit access to the computer and other system resources to only authorized users. Most operating systems also include other security features, such as an integrated firewall to protect against unauthorized access via the Internet or an option to download and install security patches (small program updates that correct known security problems) automatically from the operating system’s manufacturer on a regular basis.

Processing Techniques for Increased Efficiency

  • Operating systems often utilize various processing techniques in order to operate more efficiently and increase the amount of processing the computer can perform in any given time period. Some of the techniques most commonly used by operating systems to increase efficiency are:
  • Multitasking, Multi threading and Multiprocessing, Parallel Processing, Memory Management, Buffering and Spooling


  • Multitasking refers to the ability of an operating system to have more than one program (also called a task) open at one time. For example, multitasking allows a user to edit a spreadsheet file in one window while loading a Web page in another window or to retrieve new e-mail messages in one window while a word processing document is open in another window. Without the ability to multitask, an operating system would require the user to close one program before opening another program.

Multi threading

  • A thread is a sequence of instructions within a program that is independent of other threads, such as spell checking, printing, and opening documents in a word processing program. Operating systems that support multi threading have the ability to rotate between multiple threads (similar to the way multitasking can rotate between multiple programs) so that processing is completed faster and more efficiently, even though only one thread is executed by a single core at one time. Most operating systems support multi threading.

Multiprocessing and Parallel Processing:

  • Both Multiprocessing and Parallel processing involve using two or more CPUs (or multiple cores in a single CPU) in one computer to perform work more efficiently.
  • The primary difference between these two techniques is that, with multiprocessing, each CPU or core typically works on a different job; with parallel processing, the CPUs or cores usually work together to complete one job more quickly.
  • In either case, tasks are performed simultaneously (at exactly the same time in contrast, multitasking and multithreading use a single CPU or core and process tasks sequentially (by rotating through tasks).
  • Multiprocessing is supported by most operating systems and is used with personal computers that have multi-core CPUs as well as with servers and mainframe computers that have multi-core CPUs and/or multiple CPUs.
  • Parallel processing is used most often with supercomputers.

Memory Management:

  • Because many of today’s programs are memory intensive, good memory management, which involves optimizing the use of main memory (RAM), can help speed up processing. The operating system allocates RAM to programs as needed and then reclaims that memory when the program is closed. Because each additional running program or open window consumes memory, users can also help with memory management by limiting the number of start-up programs to only the ones that are absolutely necessary, as well as by closing windows when they are no longer needed
  • . One memory-management technique frequently used by operating systems is virtual memory, which uses a portion of the computer’s hard drive as additional RAM. When the amount of RAM required exceeds the amount of RAM available, the operating system moves pages from RAM to the virtual memory area of the hard drive

Buffering and Spooling

  • Some input and output devices are exceedingly slow, compared to today’s CPUs. If the CPU had to wait for these slower devices to finish their work, the computer system would experience a horrendous bottleneck.
  • For example, suppose a user sends a 100-page document to the printer. Assuming the printer can output 20 pages per minute, it would take 5 minutes for the document to finish printing.
  • If the CPU had to wait for the print job to be completed before performing other tasks, the computer would be tied up for 5 minutes. To avoid this problem, most operating systems use buffering and spooling.
  • A buffer is an area in RAM or on the hard drive designated to hold data that is used by different hardware devices or programs that may operate at different speeds.
  • For instance, a keyboard buffer stores characters as they are entered via the keyboard, and a print buffer stores documents that are waiting to be printed.
  • The process of placing items in a buffer so they can be retrieved by the appropriate device when needed is called buffering or spooling.

Differences among Operating Systems

  • There are different types of Operating Systems available to meet different needs.
  • Some of the major distinctions among operating systems include the type of user interface utilized, the category of device the operating system will be used with, and the type of processing the operating system is designed for.

Command Line Interface vs. Graphical User Interface

  • A user interface is the manner in which an operating system interacts with its users. Most operating systems today use a Graphical User Interface (GUI).
  • The older DOS operating system and some versions of the UNIX and Linux operating systems use a Command Line Interface (CLI), although graphical versions of UNIX and Linux are available.
  • Command line interfaces require users to input commands using the keyboard; graphical user interfaces allow the user to issue commands by selecting icons, buttons, menu items, and other graphical objects—typically with a mouse, stylus, or finger.

Examples of Operating Systems

  • Many Operating Systems today are designed either for personal computers (such as desktop and notebook computers) or for network servers. The most widely used personal and server operating systems are listed below. Mobile and embedded versions of these operating systems are also listed.

Operating Systems for Personal Computers and Server

1.Disk Operating System (DOS)

2.Windows (Windows have several versions like Windows Vista, Windows XP, Windows 7, Windows 8, Windows 10)

3.Mac OS



6.Chrome OS

7. Mobile Linux

Operating Systems for Mobile Devices include:

  • Windows
  • Android
  • Apple iOS
  • BlackBerry OS

Features of Operating Systems

  • Operating systems have some features that help them to function properly. Some of these features are:
  • Menus: Menus are a list of commands or choices offered to the user through the menu bar. Menus are used in GUI operating systems to allow the user access to program features.
  • Windows: A window is a separate viewing area on a computer display screen in a system that allows multiple viewing areas as part of a GUI. Windows are managed by a windows manager as part of a windowing system. A window can usually be resized by the user.
  • Icons: In a GUI, an icon is an image that represents an application, a capability or some other concept or entity with meaning for the user. An icon is usually selectable but can also be a non-selectable image such as a company’s logo.
  • Dialogue boxes: A dialogue box is a graphical control element in the form of a small window that communicates information to the user and prompts them for a response.
  • Files: A file is an object on a computer that stores data, information, settings or commands used with a computer program. In a GUI, files display as icons that relate to the program that opens the file. A file is the common storage unit in a computer and all programs and data are written into a file and read from a file.
  • Folders: A folder is a storage space where many files can be placed into groups and organise the computer. A folder hold one or more files and can be empty until it is filled. A folder can also contain other folders. Folders within a folder are known as subfolders.
  • File Explorer: File explorer is a GUI component that enables users to access, edit and manage data files and other and otter content stored on a computer or mobile device.
  • Accessories: Operating systems come with some handy applications known as accessories. Calculator, Notepad, Paint, Explorer, WordPad are some of the most frequently used accessories
  • Help Facility: The help facility in an OS is a documentation component that explains the features and helps the user to understand its capabilities.
  • Control Panel Menu: The control panel menu on an OS is s feature of the OS that allows the user to modify systems settings and controls. It includes several small applications that can be used to view and change hardware or software settings.
  • Print menu: discuss this with your group members
  • Accessories: Operating systems come with some handy applications known as accessories. Calculator, Notepad, Paint, Explorer, WordPad are some of the most frequently used accessories

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