OPERATING SYSTEMS & UTILITY PROGRAMS

Transcription

1 OPERATING SYSTEMS & UTILITY PROGRAMS System Software System software consists of the programs that control the operations of the computer and its devices. Functions that system software performs include: Starting up the computer. Opening, executing, and running applications. Storing, retrieving, and copying files. Formatting disks. Reducing file sizes. Backing up the contents of a hard disk. Serves as the interface between the user, the application software, and the computer s hardware. The two types of system software are operating systems and utility programs. Operating Systems An operating system (OS) is a set of programs containing instructions that coordinate all of the activities among computer hardware resources. A computer cannot function without an operating system. An operation system also contains instructions that allow a user to run application software. Application software is written to run with particular operating systems. The operating system is sometimes called the software platform. Cross-platform applications run identically on more than one operating system. The kernel, or core, of an operating system is responsible for managing memory, files, and devices; maintaining the computer s clock; starting applications; and assigning the computer s resources. The kernel and other frequently used instructions in the operating system are copied from the storage (e.g., hard disk) to the computer s memory each time when the computer is started up. Any program or command that remains in memory while the computer is running (e.g., the operating system kernel) is called memory-resident. Page 1

2 User Interfaces A user interface is the part of the software with which a user interacts. It controls how data and instructions are entered and information is presented on the screen. Two types of user interfaces are command-line interface and graphical user interface. Command-line Interface With a command-line interface, a user type keywords or press special keys on the keyboard to enter data and instructions. The set of commands a user uses to interact with the computer is called the command language. Graphical User Interface A graphical user interface (GUI) allows a user to use menus and visual images such as icons, buttons, and other graphical objects to issue commands. A menu displays a set of available commands or options from which a user chooses one or more. An icon is a small image that represents an item such as a program, an instruction, or a file. Graphical user interfaces are described as user-friendly, because they are the easiest to learn and work with. Features of Operating Systems A single user operating system allows only one user to run one program at a time. A multitasking operating system allows a single user to work on two or more applications that reside in memory at the same time. A multiuser operating system enables two or more users to run a program simultaneously. A multiprocessing operating system can support two or more CPUs running programs at the same time. A single operating system may support one or all of above capabilities. Functions of an Operating System Memory Management The purpose of memory management is to optimize use of RAM. The OS has to allocate, or assign items to areas of memory, called buffers, while they are being processed; to monitor carefully the Page 2

3 contents of these items in memory; and to clear these items from memory when they are no longer required by the CPU. A buffer is an area of memory or storage in which data and information is placed while waiting to be transferred to or from an input or output device. Some operating systems use virtual memory to optimize RAM. With virtual memory (VM), the operating system allocates a portion of a storage medium, usually the hard disk, to function as additional RAM. The area of the hard disk used for virtual memory is called a swap file. The amount of data and program instructions swapped or exchanged at a given time is called a page. Paging is the technique of swapping items between memory and storage. Trashing occurs when an operating system spends much of its time paging, instead of executing application software. The computer needs to install more RAM if trashing occurs frequently. Spooling Print Jobs A print job is the document being printed by an application. With spooling, the print jobs are placed in a buffer instead of being sent immediately to the printer. As soon as the print job is placed in the buffer, the CPU is available to process the next instruction and the computer can be used for other tasks. Multiple print jobs are queued, or line up, in the buffer and the program that manages and intercepts print jobs and places them in the queue is called the print spooler. Configuring Devices A device driver is a small program that accepts commands from another program and then converts these commands into commands that the device understands. Plug and Play is the computer s capability of recognizing any new device and assisting in the installation of the device by loading the necessary drivers automatically and checking for conflicts with other devices. In the past, installing a new device often required setting switches and other elements on the motherboard. Page 3

4 Occasionally, a user needs to know which interrupt request the device should use for communications. An interrupt request (IRQ) is a communications line between a device and the CPU. Most computers have 15 IRQs. With Plug and Play, the OS determines the best IRQ to use for the communications. An IRQ conflict occurs if the OS uses an IRQ that already is assigned to another device. Monitoring System Performance A performance monitor is a program that accesses and reports information about various system resources and devices. The information in such reports can help a user identify problems with resources. Administering Security Log on is the process of entering a user name and a password into the computer. Most multiuser operating systems require each user to log on. A user name, or user ID, is a unique combination of characters that identifies one specific user. A password is a combination of characters associated with a user name that allow a user to access certain computer resources. Both successful and unsuccessful log on attempts are often recorded in a file so the system administrator can review who is using or attempting to use the computer. Some operating systems also allow a user to assign passwords to files so that only authorized users can open them. Managing Storage Media and Files A file manager is a program that performs functions related to storage and file management. Functions performed by a file manager include: Formatting and copying disks. Displaying a list of files on a storage medium. Checking the amount of used or free space on a storage medium. Copying, renaming, deleting, moving, and sorting files. Page 4

5 Popular Operating Systems Many of the first operating systems were device dependent. Device dependent operating systems were developed by manufacturers specifically for the computers in their product line. Proprietary software is software that is privately owned and limited to a specific vendor or computer model. Device independent operating systems will run on many manufacturers computers. A downward-compatible operating system is one that recognizes and works with application software that was written for an earlier version of the operating system. Upward compatible application software was software written for an earlier version of the operating system, but runs under the new version. The trend today is towards device-independent operating systems. Some of the more popular operating systems are: DOS DOS (Disk Operating System) refers to several single user operating systems that were developed in the early 1980s form PCs. The two more widely used versions of DOS were PC-DOS and MS-DOS, both developed by Microsoft. Microsoft developed PC-DOS for IBM, which installed and sold the OS with their computers. Microsoft marketed and sold MS-DOS to makers of IBM-compatible PCs. Earlier versions of DOS used a command-line interface. Later versions of DOS included also a menu-driven user interface, as well as improved memory and disk management. DOS is not widely used today because it does not offer a graphical user interface and it cannot take full advantage of modern 32-bit microprocessors. Windows 3.x Windows 3.x refers to three early versions of Microsoft Windows: Windows 3.0, Windows 3.1, and Windows These Windows 3.x versions were not actually operating systems, but operating environments. An operating environment is a graphical user interface that works in combination with an operating system (in this case DOS). Page 5

6 Windows 95 Windows 95 is a true multitasking operating system that does not require DOS to run. Advantages of Windows 95 include: An improved graphical user interface. Includes some DOS and Windows 3.x features to allow for downward compatibility. Most programs run faster under the OS. Take advantage of 32-bit processors. Supports a more efficient form of multitasking. Supports networking, Plug and Play, longer file names, and . Windows NT Windows NT is an operating system designed for client-server networks. The server uses a version called Windows NT server. The clients connect to the server using a version called Windows NT Workstation, which has a Windows 95 interface. Windows 98 Windows 98 is an upgrade to the Windows 95 operating system. Advantages of Windows 98 include: More integrated with the Internet. Includes the Active Desktop interface option, which allows a user to set up Windows so that icons on the desktop and file names in Windows Explorer work like Web links. Provides faster system startup and shutdown. Better file management. Supports for new multimedia technologies such as DVD and WebTV. Supports the Universal Serial Bus (USB). Like Windows 95, Windows 98 can run 16- and 32-bit software. Windows 2000 Windows 2000 is an upgrade to the Windows 98 and Windows NT operating systems. Two basic versions of Windows 2000 are the Windows 2000 Server family, and the Windows 2000 Professional. The Windows 2000 Server family includes Windows 2000 Server, Windows 2000 Advanced Server, and Windows 2000 Datacenter Server, for various levels of network servers. Page 6

7 Windows 2000 Professional is a stand-alone version for business desktop or laptop computers, as well as for computers connected to the networks. Windows Millennium Windows Millennium is an updated version of Windows 98 for the consumer that uses a computer to surf the Internet or for entertainment. Whereas Windows 2000 is an operating system designed for business users, Windows Millennium is designed for home users. Windows CE Windows CE is a scaled-down Windows operating system designed for use on wireless communication devices and handheld computers. Palm OS Palm OS is an operating system for PDAs that can manage schedules and contacts and easily synchronize this information with a desktop computer. Mac OS Mac OS was the first commercially successfully graphical user interface. It was released with the Apple s Macintosh computers in 1984 and has set the standard for the graphical user interface for non-macintosh systems. The Mac OS is available only on computers manufactured by Apple. However, it has the capability of opening, editing, and saving files created using the Windows and DOS platforms. OS/2 OS/2 is IBM s multitasking graphical user interface operating system designed to work with 32-bit microprocessors. OS/2 can also run programs written for DOS and most Windows 3.x programs. UNIX UNIX is a multiuser, multitasking operating system developed in the early 1970s by scientists at Bell Laboratories. Today, a version of UNIX is available for most computers of all sizes. UNIX is capable of handling a high volume of transactions ina multiuser environment and working with multiple CPUs using multiprocessing. Thus, UNIX is used most often on workstations and servers. A weakness of UNIX is that it has a command-line interface, and many of its commands are difficult to remember and use. Page 7

8 Some versions of UNIX, however, such a the version for the Apple Macintosh, offer a graphical user interface. Linux Linux is a popular, free UNIX-like GUI operating system. Linux is open-source software, which means its code is made available to the public. Customers can personalize the software to meet their needs, and users that modify the software share their improvements with others. NetWare Novell s NetWare is a widely used network operating system designed for client-server networks. Starting a Computer Booting is the process of starting or resetting a computer, which involves loading an operating system into memory. A cold boot is when a computer is turned on after it has been powered off completely. A warm boot is the process of restarting, or resetting, a computer that is already on. When using Windows, a warm boot can be performed by pressing the key combinations CTRL+ALT+DEL. The steps that occur during a cold boot using the Windows operating system: 1. The power supply sends an electrical signal to the motherboard and other devices located in the system unit. 2. The CPU resets itself and looks for the ROM that contains the BIOS. The BIOS (basic input/output system), is firmware that contains the computer s startup instructions. 3. The BIOS executes the power-on self test (POST) to make sure that the computer hardware is connected properly and operating correctly. The POST checks the various system components such as the buses, system clock, expansion cards, RAM chips, keyboard, floppy disk drive, and hard disk. 4. The results of the POST are compared with data in a CMOS (complementary metal-oxide semiconductor) chip on the motherboard. Page 8

9 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 needed when the computer is turned on. The CMOS chip is updated whenever new components are installed. If any problems are found, the computer may beep, display error message, or cease operating depending on the severity of the problem. 5. If the POST is completed successfully, the BIOS looks for the boot program that loads the operating system. 6. Once located, the boot program is loaded into memory and executed, which then loads the kernel of the operating system into RAM. 7. The operating system loads system configuration information and the remainder of the operating system is loaded into RAM and the desktop and the icons display on the screen. In Windows, system configuration information is contained in several files called the registry. A boot disk is a floppy disk that contains certain operating system commands that will start the computer. Utilities Programs A utility program or utility is a type of system software that performs a specific task, usually related to managing a computer, its devices, or its programs. A file viewer is a utility that displays the contents of a file. Windows Explorer has two viewers: one called Quick View to display the contents of text files and another called Imaging Preview for graphics files. A file compression utility reduces, or compresses, the size of a file. A compressed file takes up less storage space on a hard disk or floppy disk, which frees up room on the disk and improves system performance. Compressed files sometimes are called zipped files because they usually have a.zip extension. A compressed file must be unzipped or restored to its original form. A diagnostic utility compiles technical information about a computer s hardware and certain system software programs and then prepares a report outlining any identified problems. Windows 98 includes a diagnostic utility called Dr. Watson. Page 9

10 A disk scanner is a utility that detects and corrects both physical and logical problems on a hard disk or floppy disk, and searches for and removes unwanted files. A physical problem is one with the media, such as a scratch on the surface of the disk. A logical problem is one with the data, such as a corrupted file allocation table (FAT). A disk defragmenter is a utility that reorganizes the files and unused space on a computer s hard disk so data can be accessed more quickly and programs can run faster. When the contents of a file are scattered across two or more noncontiguous sectors, the file is fragmented. The process of defragmentation is reorganizing the disk so the files are stored in contiguous sectors. Windows 98 includes a disk defragmenter, called Disk Defragmenter. An uninstaller is a utility that removes an application, as well as any associated entries in the system files. A backup utility allows a user to copy, or backup, selected files or the entire hard disk onto another disk or tape. Backup files are usually not usable in their backup form because many backup programs will compress the files during the backup process. A restore program that is included with the backup utility reverses the process and returns backed up files to their original form. An antivirus program is a utility that prevents, detects, and removes viruses from a computer s memory or storage devices. A virus is a program that copies itself into other programs and spreads through multiple computers. Viruses are often designed to damage a computer intentionally by destroying or corrupting its data. A screen saver is a utility that causes the monitor s screen to display a moving image or blank screen if no keyboard or mouse activity occurs for a specified time period. Screen savers originally were developed to prevent a problem called ghosting, in which images could be permanently etched on a monitor s screen. Screen savers can also be used for reasons of security, business, or entertainment. Page 10