Computer Operating Systems

ICT 100: Introduction to Information and Communications Technology Unit 3: Operating Systems Objectives: ? ? ? ? ? ? ? Define the term software Differentiate between system software and application software Define the terms operating system and utility program Identify the types of operating systems Explain the boot process of a computer Describe the functions of an operating system Identify common utility programs Software, also called a program, consists of a series of related instructions, organized for a common purpose, that tells the computer what tasks to perform and how to perform them.
The two categories of software are system software and application software. System Software System software consists of the programs that control or maintain the operations of the computer and its devices. System software serves as the interface between the user, the application software, and the computer’s hardware. It includes the following: 1. Operating Systems 2. Library Programs 3. Utility Programs Operating Systems An operating system (OS) is a set of programs containing instructions that work together to coordinate all the activities among computer hardware resources.
Every computer needs an operating system to act as an interface between the user and the computer hardware. It allows the user to perform tasks without having to know how they are done. For example, a user can give a command to save a file on disk without having to know where the file will be stored or how it will be retrieved again. When a command is given to print a document, the user does not have to be concerned with the details of how the printer works – a program called a device driver takes care of the details. ICT 100 – Operating Systems Page 1 of 9

The operating system that a computer uses sometimes is called the platform. With purchased application software, the package or specifications identify the required platform (operating system). A cross-platform program is one that runs the same on multiple operating systems. Application programs are usually written to work with a particular operating system, so that a word processor, which works with Windows, will not work on an Apple Mac, which has a different operating system. When purchasing application software, ensure that it works with the operating system installed on your computer or mobile device.
The Bootstrap Process The process of starting or restarting a computer is called booting. When turning on a computer that has been powered off completely, you are performing a cold boot. A warm boot is the process of using the operating system to restart a computer. A warm boot properly closes any running processes and programs; however, it does not save any unsaved work. Thus, always remember to save your work before rebooting (restarting) a computer. Each time you boot a computer, the kernel and other frequently used operating system instructions are loaded, or copied, from storage into the computer’s memory (RAM).
The kernel is the core of an operating system that manages memory and devices, maintains the computer’s clock, starts programs, and assigns the computer’s resources, such as devices, programs, data, and information. The kernel is memory resident, which means it remains in memory while the computer is running. Other parts of the operating system are nonresident, that is, these instructions remain on a storage medium until they are needed. When you boot a computer, a series of messages may appear on the screen. The actual information displayed varies depending on the make and type of the computer and the equipment installed.
The boot process, however, is similar for large and small computers. The steps of the bootstrap process are given and explained below: Step 1: The power supply sends a signal to the components in the system unit. When you turn on the computer, the power supply sends an electrical signal to the components in the system unit. Step 2: The processor finds the ROM chip(s) that contains the BIOS. The charge of electricity causes the processor chip to reset itself and find the ROM chip(s) that contains the BIOS. The BIOS (pronounced BYE-ose), which stands for basic input/output system, is firmware that contains the computer’s start-up instructions.
ICT 100 – Operating Systems Page 2 of 9 Step 3: The BIOS performs the POST, which checks components, such as the mouse, keyboard, and adapter cards. The BIOS executes a series of tests to make sure the computer hardware is connected properly and operating correctly. The tests, collectively called the power-on self test (POST ), check the various system components including the buses, system clock, adapter cards, RAM chips, mouse, keyboard, and drives. As the POST executes, LEDs (tiny lights) flicker on devices such as the disk drives and keyboard.
Beeps also may sound, and messages may appear on the screen. Step 4: The results of the POST are compared with data in a CMOS chip. The POST results are compared with data in a CMOS chip. CMOS is a technology that uses battery power to retain information when the computer is off. The CMOS chip stores configuration information about the computer, such as the amount of memory; type of disk drives, keyboard, and monitor; the current date and time; and other startup information. It also detects any new devices connected to the computer.
If any problems are identified, the computer may beep, display error messages, or cease operating — depending on the severity of the problem. Step 5: The BIOS may look for the system files on a USB flash drive or on an optical disc drive or may look directly on drive C (hard disk). If the POST completes successfully, the BIOS searches for specific operating system files called system files. The BIOS may look first to see if a USB flash drive plugged in a USB port or a disc in an optical disc drive contains the system files, or it may look directly on drive C (the designation usually iven to the first hard disk) for the system files. Step 6: The system files and the kernel of the operating system load into memory (RAM) from storage (i. e. , hard disk). Once located, the system files load into memory (RAM) from storage (usually the hard disk) and execute. Next, the kernel of the operating system loads into memory. Then, the operating system in memory takes control of the computer. Step 7: The operating system loads configuration information, may request user information, starts several background processes, and displays the desktop on the screen. The operating system loads system configuration information.
Necessary operating system files are loaded into memory. On some computers, the operating system verifies that the person attempting to use the computer is a legitimate user. Finally, the desktop and icons are displayed on the screen. The operating system executes programs in the Startup folder, which contains a list of programs that open automatically when you boot the computer. ICT 100 – Operating Systems Page 3 of 9 Figure 1 The bootstrap process Shut down options including powering off the computer, placing the computer in sleep mode, and hibernating the computer.
Sleep mode saves any open documents and programs to RAM, turns off all unneeded functions, and then places the computer in a low-power state. If, for some reason, power is removed from a computer that is in sleep mode, any unsaved work could be lost. Hibernate, by contrast, saves any open documents and programs to a hard disk before removing power from the computer. Operating System Functions Operating systems perform the following functions: (1) manage resources, (2) manage backing store, (3) handle interrupts, (4) provides a user interface, (5) provide networking capabilities, (6) provide security. . Manage Resources The operating system keeps track of all resources (CPU, disk, memory, files, input and output devices etc. ). Through scheduling it decides what process gets what resource, when it gets it, ICT 100 – Operating Systems Page 4 of 9 how much and for how long. This is called allocation of resources. Resources can also be taken away from a process. This is called de-allocation of resources. Memory Management Computers are capable of holding several programs in memory simultaneously so that a user can switch from one application to another.
The purpose of memory management is to optimize the use of random access memory (RAM). The operating system allocates, or assigns, data and instructions to an area of memory while they are being processed. Then, it carefully monitors the contents of memory. Finally, the operating system releases these items from being monitored in memory when the processor no longer requires them. If there is no memory management then one program might accidentally address the memory space occupied by another. This would result in corrupting programs with potentially disastrous results.
Virtual memory is used when sufficient physical RAM is not available. Part of a hard disk is allocated to be used as if it were main memory. The speed of access is very slow compared to RAM access speed. File Management The file management part of an operating system has four basic functions: 1. To allocate space on the storage device to hold each file stored, and to deallocate space when a file is deleted. Space is usually divided into fixed size allocation units (addressable blocks) of say 512 or 1024 bytes. 2. To keep track of the allocation units occupied by each file.
Files may be split over several allocation units, not necessarily contiguous (i. e. together). A file may initially occupy one unit of 512 bytes, and then when updated by a user, need extra space which may have to be found somewhere else on the disk. 3. To control file access rights and permissions. 4. To map logical file addresses to physical addresses. For example, a physical disk may be split into several logical drives C, D, E, F, G. Managing Programs Some operating systems support a single user and only one running program at a time. Others support thousands of users running multiple programs.
How an operating system handles programs directly affects your productivity. A single user/single tasking operating system allows only one user to run one program at a time. A single user/multitasking operating system allows a single user to work on two or more programs that reside in memory at the same time. When a computer is running multiple programs concurrently, one program is in the foreground and the others are in the background. ICT 100 – Operating Systems Page 5 of 9 The one in the foreground is the active program, that is, the one you currently are using.
The other programs running but not in use are in the background. A multiuser operating system enables two or more users to run programs simultaneously. Networks, servers, mainframes, and super computers allow hundreds to thousands of users to connect at the same time, and thus are multiuser. A multiprocessing operating system supports two or more processors running programs at the same time. Multiprocessing involves the coordinated processing of programs by more than one processor. Multiprocessing increases a computer’s processing speed. 2.
Manage Backing Store The operating system is responsible for the transfer of data from secondary storage (e. g. disk) to memory and vice versa. It also has to maintain a directory of the disk so that files and free spaces can be quickly located. 3. Handle Interrupts The operating system detects interrupts (such as the click of the mouse or a process indicating that it is finished with the processor) and then performs the necessary task (such as allowing the processor to be used by another process). 4. Provide a User Interface You interact with software through its user interface.
That is, a user interface controls how you enter data and instructions and how information is displayed on the screen. The operating system acts as a user interface between the user and the machine. Command-Line Interface To configure devices, manage system resources, and troubleshoot network connections, network administrators and other advanced users work with a commandline interface. In a command-line interface, a user types commands or presses special keys on the keyboard (such as function keys or key combinations) to enter data and instructions. Graphical User Interface Most users today work with a graphical user interface.
With a graphical user interface (GUI), you interact with menus and visual images such as buttons and other graphical objects to issue commands. Many current GUI operating systems incorporate features similar to those of a Web browser, such as links and navigation buttons (i. e. , Back button and Forward button). Some GUI operating systems provide access to command-line interfaces. Menu-driven Interface User is presented with a range of options from which to choose ICT 100 – Operating Systems Page 6 of 9 Form Interface A user interface in which the computer outputs separate prompt and response fields for a number of inputs.
Natural Language – the interface consists of standard languages such as English, Spanish, French, and Dutch etc. 5. Provide Networking Capabilities Some operating systems have networking capabilities built in, others are creating specifically for managing networks, e. g. server operating systems. Networking capabilities include organizing and coordinating how multiple users access and share resources on a network. Resources include hardware, software, data, and information. For example, a server operating system allows multiple users to share a printer, Internet access, files, and programs.
The network administrator, the person overseeing network operations, uses the server operating system to add and remove users, computers, and other devices to and from the network. The network administrator also uses the server operating system to install software and administer network security. 6. Provide Security Computer and network administrators typically have an administrator account that enables them to access all files and programs on the computer or network, install programs, and specify settings that affect all users on a computer or network.
Settings include creating user accounts and establishing permissions. These permissions define who can access certain resources and when they can access those resources. For each user, the computer or network administrator establishes a user account, which enables a user to access, or log on to, a computer or a network. Each user account typically consists of a user name and password. A user name, or user ID, is a unique combination of characters, such as letters of the alphabet or numbers that identifies one specific user. Many users select a combination of their first and last names as their user name.
A user named Henry Baker might choose HBaker as his user name. A password is a private combination of characters associated with the user name that allows access to certain computer resources. Some operating systems allow the computer or network administrator to assign passwords to files and commands, restricting access to only authorized users. After entering a user name and password, the operating system compares the user’s entry with a list of authorized user names and passwords. If the entry matches the user name and password ICT 100 – Operating Systems Page 7 of 9 ept on file, the operating system grants the user access. If the entry does not match, the operating system denies access to the user. To protect sensitive data and information further as it travels over a network, the operating system may encrypt it. Encryption is the process of encoding data and information into an unreadable form. Administrators can specify that data be encrypted as it travels over a network to prevent unauthorized users from reading the data. When an authorized user attempts to read the data, it automatically is decrypted, or converted back into a readable form. Types of Operating Systems
Operating systems can be divided into the three following types: 1. Stand-alone 2. Server 3. Embedded Stand-Alone Operating System A stand-alone operating system is a complete operating system that works on a desktop computer, notebook computer, or mobile computing device. Some stand-alone operating systems can work in conjunction with a server operating system (here it functions as a client operating system); others include networking capabilities allowing users to set up small networks (e. g. home or small business network). Examples of currently used stand-alone operating systems are Windows 7, Mac OS X, UNIX, and Linux.
Server Operating System A server operating system is an operating system that is designed specifically to support a network. These operating systems can support all sizes of networks from small to large-sized networks and Web servers. A server operating system typically resides on a server and provides client machines with access to resources. Examples of server operating systems include Windows Server 2008, UNIX, Linux, Solaris, and NetWare. Embedded Operating System The operating system on mobile devices and many consumer electronics, called an embedded operating system, resides on a ROM chip.
Most handheld computers and small devices use embedded operating systems. Popular embedded operating systems today include Windows Embedded CE, Windows Mobile, Palm OS, iPhone OS, BlackBerry, Google Android, embedded Linux, and Symbian OS. ICT 100 – Operating Systems Page 8 of 9 Library Programs A library program is available to all users of a multi-user computer system, typically to carry out common tasks required by everyone. For example a routine that searches for lost files or restores corrupted files may be stored in a library. Utility Programs
A utility program, also called a utility, is a type of system software that allows a user to perform maintenance-type tasks, usually related to managing a computer, its devices, or its programs. Most operating systems include several built-in utility programs. Users can also buy stand-alone utility programs. Utility programs perform common tasks that thousands of computer users need to do at some time or another, such as searching for files, viewing images, backing up files and disks, uninstalling programs, defragmenting disks, burning optical discs, and so on.
One common utility is compression software such as WinZip that ‘zips’ files so that they occupy less space. This is very useful if your want to transmit a graphic or large data file over the Internet, as the transmission time will be much reduced. References Shelly, G. B, Vermaat, M. E. (2010). Discovering Computers 2011. Boston, MA: Course Technology Daley, B. (2008). Computers Are Your Future 2007. Upper Saddle River, NJ: Pearson Education Heathcote, P. M, Langfield, S. (2004). ‘A’ Level Computing, 5th edition. Oxford: Payne-Gallway Publishers Ltd ICT 100 – Operating Systems Page 9 of 9

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