1. Chapter 8 Computer Software

2. What Types of Software Make a Computer Useful?

3. Objectives
Understand the scope of knowledge needed to interact effectively with a computer.
Understand the two basic types of software used in the operation of a computer.

4. Interactive With the System
To interact effectively with a computer, user needs to be knowledgeable in four areas:
General software concepts (for example, windows, menus, uploading, and so on).
The operation and use of the hardware over which you have control (such as the PC, magnetic disk, and printer).
The function and use of the computer's operating system and/or its graphical user interface (GUI), both of which provide a link between the user, the computer system, and the various applications.
The specific applications programs you are using.

5. Interactive With the System (continued)
The first three areas are prerequisites to the fourth because you will need a
working knowledge of software concepts,
hardware, and
the operating system and/or a GUI
before you can make effective use of
Quicken (accounting),
Harvard Graphics (presentation graphics),
Paradox (database).

6. Categories of Software
Computer hardware cannot perform alone.
Software refers to the instructions that direct the operations of a computer.
There are two basic types of software:
system software (controls hardware)
application software (performs specific tasks).

7. Categories of Software(continued)
System software tells the computer how to operate.
System software is a collection of programs that starts the computer and coordinates all the activities of the computer system.
It does not accomplish specific tasks for a user, such as creating documents or analyzing data.

8. Categories of Software(continued)
System software includes
Operating systems (the most important type of system software),
Data management software,
Computer language-oriented software, and
Utilities that help users perform various functions.

9. Categories of Software(continued)
A principal component of system software is the operating system.
Data management software includes
database and file management programs that manage data for an operating system.
Computer language-oriented software includes
language translators such as assemblers, interpreters, and compilers .
program generators (programs that automatically generate program code), debugging and testing programs.

10. Categories of Software(continued)
Utilities are programs that are purchased as separate products; they perform a wide range of functions. This type of software includes products such as
data conversion programs that convert data from one format to another,
data recovery programs that restore damaged or accidentally erased data,
librarians that log and track the locations of disk or tape program files,
security and auditing programs, and
merge and sort programs.

11. Categories of Software(continued)
Application software refers to programs that allow you to accomplish specific tasks, like creating a document, organizing data, or drawing graphs.
Software acts as a connection, or interface, between you and the hardware.
Interface is a term that describes how two parts are joined so that they can work together.
System software and application software provide an interface to the hardware.

12. Categories of Software(continued)
Figure 8.1 shows the functional relationship among system software, application software, hardware, and a user.
User
System software
Hardware
Application software
Figure The Relationship Among System Software, Application Software, Hardware, and a User

13. Operating System

14. Objectives
Define operating system, describe the major functions, and discuss several ways it is typically used in the day-to-day operation of a computer.
Describe several capabilities of operating systems.
Contrast three types of user interfaces.
Describe the characteristics and functionality of a graphical user interface (GUI).
Understand the purpose of a disk operating system and an operating environment, and identify four major microcomputer operating systems and their associated environments.

15. What Is an Operating System?
An operating system layer, designed to be invisible to the user, lays between the application software and hardware.
An operating system (OS) is a core set of programs that control and supervise the hardware resources of a computer and provide services to other system software, application software, programmers, and users of a computer.

16. What Is an Operating System? (continued)
The OS gives the computer the instructions it needs to operate, telling it how to interact with hardware, other software, and the user.
The OS establishes a standard interface, or means of communication, between users and their computer systems.
When you power up a computer, you boot the system.
The booting procedure is so named because the computer "pulls itself up by its own bootstraps" (without the assistance of humans).

17. What Is an Operating System? (continued)
When booting the system,
First, a program in read-only memory (ROM) initializes the system and runs a system check to verify that the electronic components are operational and readies the computer for processing.
Next, the operating system is loaded to RAM, takes control of the system, and presents the user with a system prompt or a GUI screen full of options.

18. Operating System Parts
Operating systems are composed of two major parts:
control programs
service programs

19. Operating System Parts (continued)
Control programs manage computer hardware and resources.
The main program in most operating systems is the supervisor program.
A supervisor program is a control program that is known in some operating systems as the monitor, executive, or kernel.
The supervisor program is responsible for controlling all other OS programs as well as other system and application programs.
The supervisor program controls the activities of all of the hardware components of a computer.

20. Operating System Parts (continued)
Service programs are external OS programs that provides a service to the user or programmer of a computer.
They must be loaded separately because they are not automatically loaded when the operating system is loaded.
They perform routine but essential functions, such as formatting a disk for use and copying files from one location to another.

21. Operating System Functions
In order to meet the dual requirements of providing support for common computer system tasks and hardware independence, operating systems perform these four important functions:
Manage the allocation of main memory
Coordinate processing tasks
Schedule the use of peripheral devices, such as secondary storage devices and printers
Monitor the use of all equipment

22. Managing Memory
Memory management includes protecting programs in memory from accidental erasure and accommodating programs that exceed the physical limitations of main memory.
An OS (operating system) keeps track of its own location and how much main memory it occupies and prohibits other programs and data from being stored in its space.

23. Coordinating Processing Tasks
A job is a computerized task.
A job is a collection of one or more related programs and their data.
Each job requires use of the processor, main memory, and secondary storage devices.
Many modern operating systems make it possible to schedule a job for processing based on it’s priority and it’s computer systems resource requirements.
In the mainframe computer environment, each job to be processed includes a group of instructions written in a special language called job control language (JCL).

24. Large Computer Systems

25. Managing Resources Operating systems manage computer resources by:
Keeping track of computer access and usage
Keeping track of peripheral device usage
Providing up-to-date reports of system utilization costs
Access to and usage of a computer system can be monitored (through the use of a run log) for security and control - to prevent unauthorized access to, and use of, a computer system and user files.

26. Typical Day-to-Day Uses of an Operating System
Executing application programs.
Formatting floppy diskettes.
Setting up directories to organize your files.
Displaying a list of files stored on a particular disk.
Verifying that there is enough room on a disk to save a file.
Protecting and backing up your files by copying them to other disks for safekeeping.

27. Typical Day-to-Day Uses of an Operating System (continued)
Computer housekeeping operations such as erasing old files that are no longer needed, moving files from one directory to another for better organization, and renaming files to make their content more evident.

28. How Do Operating Systems Differ?
Operating systems for large computers are more complex and sophisticated than those for microcomputers because the operating systems for large computers must address the needs of a very large number of users, application programs, and hardware devices, as well as supply a host of administrative and security features.

29. How Do Operating Systems Differ? (continued)
Early computers used serial processing operating systems, which meant the computer was capable of processing only one job at a time.
Modern operating systems allow computer to run two or more programs simultaneously. They are called multiprogramming operating systems. Several techniques are used to accomplish this, including:
multitasking
time sharing
multiprocessing

30. How Do Operating Systems Differ? (continued)
Multitasking
Multitasking means that a single user can run more than one job at a time.
In a multitasking system, main memory is usually partitioned into segments for storing the user programs and their associated data separately.

31. How Do Operating Systems Differ? (continued)
Time Sharing
Time sharing is a multiprogramming technique that makes multiple programs appear to run at the same time by allocating short periods of CPU time to each of the programs on a rotating basis.
A major benefit of time sharing is that users with small programs do not have to wait for the CPU to come to a logical stopping point in large, complicated programs.
Under time sharing, no single program is allowed to dominate the CPU’s time.

32. How Do Operating Systems Differ? (continued)
Multiprocessing
Multiprocessing is possible when a computer system consists of two or more processors.
Multiple processors share the workload of a computer system

33. How Do Operating Systems Differ? (continued)
Operating system capabilities can be described in terms of
the number of users they can accommodate at one time,
how many tasks can be run at one time, and
how they process those tasks.

34. Number of Users
A single-user operating system allows only one user at a time to access a computer.
Most operating systems on microcomputers, such as DOS and Window 95, 98, are single-user access systems.

35. Number of Users (continued)
A multiuser operating system allows two or more users to access a computer at the same time (UNIX).
The actual number of users depends on the hardware and the OS design.
Time sharing allows many users to access a single computer.
This capability is typically found on large computer operating systems where many users need access at the same time.

36. Number of Tasks
A single tasking operating system allows only one program to execute at a time, and the program must finish executing completely before the next program can begin.

37. Number of Tasks (continued)
A multitasking operating system allows a single CPU to execute what appears to be more than one program at a time. Several techniques are used to accomplish this, including:
Context switching
Cooperative multitasking
Time-slice multitasking
Multithreading supports

38. Number of Tasks (continued)
Context switching
allows several programs to reside in memory but only one to be active at a time. The active program is said to be in the foreground. The other programs in memory are not active and are said to be in the background. Instead of having to quit a program and load another, you can simply switch the active program in the foreground to the background and bring a program from the background into the foreground with a few keystrokes.

39. Number of Tasks (continued)
Cooperative multitasking
in which a background program uses the CPU during idle time of the foreground program. For example, the background program might sort data while the foreground program waits for a keystroke.

40. Number of Tasks (continued)
Time-slice multitasking
enables a CPU to switch its attention between the requested tasks of two or more programs. Each task receives the attention of the CPU for a fraction of a second before the CPU moves on to the next. Depending on the application, the order in which tasks receive CPU attention may be determined sequentially (first come first served) or by previously defined priority levels.

41. Number of Tasks (continued)
Multithreading supports
several simultaneous tasks within the same application. For example, with only one copy of a database management system in memory, one database file can be sorted while data is simultaneously entered into another database file.

42. Number of Processing Multiprocessing Interprocessing
Real-time processing
Virtual-machine (VM) processing
Virtual memory

43. Number of Processing (continued)
Multiprocessing operating system
allows the simultaneous execution of programs by a computer that has two or more CPUs. Each CPU can be either dedicated to one program, or dedicated to specific functions and then used by all programs. Several techniques are used to accomplish this, including:

44. Number of Processing (continued)
Interprocessing (dynamic linking)
is a type of processing that allows any change made in one application to be automatically reflected in any related, linked application.

45. Number of Processing (continued)
Real-time processing
allows a computer to control or monitor the performance of other machines and people by responding to input data in a specified amount of time.

46. Number of Processing (continued)
Virtual-machine (VM) processing
creates the illusion that there is more than one physical machine. VM capabilities permit a computer to run numerous operating systems at one time. VM capabilities are typically used on supercomputers and mainframes.

47. Number of Processing (continued)
Virtual memory (virtual storage)
allows you to use a secondary-storage device as an extension of main memory. Virtual memory resolves the problem of insufficient main memory to contain an entire program and its data.

48. Number of Processing (continued)
Virtual-machine (VM) processing
allows a computer to control or monitor the performance of other machines and people by responding to input data in a specified amount of time.

49. How Will I Use an Operating System?
The user interface of an operating system is the portion of the program with which users interact.
The user interface can be
Command-line,
Menu-driven, and
Graphics-based.

50. How Will I Use an Operating System? (continued)
A command-line interface requires a user to type the desired response at a prompt using a special command language.
To be an effective user of any command-line software, you must memorize its commands and their exact syntax-no easy task.
A menu-driven interface allows the user to select commands from a list (menu) using the keyboard or a pointing device such as a mouse.

51. How Will I Use an Operating System? (continued)
A graphical user interface (GUI)
The trend is away from text-based, command-line interfaces to user-friendly, graphics-oriented environment called a graphical user interface (GUI).
Graphical user interfaces rely on graphics-based software.
Graphic-based software permits the integration of text with high-resolution graphic image, called icons.
GUI users interact with the operating system and other software packages by using a pointing device and a keyboard to issue commands.

52. How Will I Use an Operating System? (continued)
Rather than enter a command directly, the user chooses from options displayed on the screen.
The equivalent of a syntax-sensitive operating system command is entered by pointing to and choosing one or more options from menu or by pointing to and choosing a graphics image, called an icon.

53. How Will I Use an Operating System? (continued)
typically GUI includes some or all of the following parts:
icons, which are graphical images that represent items, such as files and directories.
a graphical pointer, which is controlled by a pointing device (mouse), to select icons and commands and move on-screen items.
on-screen pull-down menus that appear or disappear, controlled by the pointing device.
windows that enclose applications or objects on the screen.
GUIs have effectively eliminated the need for users to memorize and enter cumbersome commands.

54. What Types of Operating Systems and Environments Are Used on Microcomputers?
A disk operating system (DOS) is an operating system that allows and manages the use of disk drives for storing and accessing data and programs.
An operating environment is software that improves its user interface and enhances the functions of an operating system.
Operating environments often use windows to allow the display of several applications on the screen concurrently and to facilitate data transfer between them.

55. What Types of Operating Systems and Environments Are Used on Microcomputers?
A disk operating system (DOS) is an operating system that allows and manages the use of disk drives for storing and accessing data and programs.
An operating environment is software that improves its user interface and enhances the functions of an operating system.
Operating environments often use windows to allow the display of several applications on the screen concurrently and to facilitate data transfer between them.

56. Operating environment
What Types of Operating Systems and Environments Are Used on Microcomputers? (continued)
The operating environment logically sits on top of the OS (See Figure 8.2).
User
Hardware
Application
software
Operating environment
Operating system
Figure The operating environment is an interface between the user and the operating system

57. What Types of Operating Systems and Environments Are Used on Microcomputers? (continued)
Popular microcomputer operating systems include MS-DOS, OS/2, the Apple Macintosh operating system, and Unix.
Popular operating environments include Microsoft's Windows for DOS; the Presentation Manager for OS/2; Finder and MultiFinder for Apple Macintosh; and OSF/Motif and SUN/OpenLook for Unix.

58. Microcomputer Operating Systems
DOS is a single-user operating system for IBM and compatible PCs that has minimal multitasking capabilities. A number of software companies have written DOS add-ons that provide virtual memory and multitasking capabilities.
Macintosh System 7 is a single-user operating system that supports multitasking and virtual memory.

59. Microcomputer Operating Systems (continued)
Up through the most current release of Windows 3, it is classified as an icon-based DOS shell program reduces the user’s need to have an in-depth knowledge of DOS to effectively use a PC.
Windows NT, on the other hand, is a 32-bit operating system with virtual memory, multitasking, and even networking capabilities built in.

60. Microcomputer Operating Systems (continued)
OS/2 is a 32-bit operating system designed for a single user working on multiple applications at once on IBM compatible personal computers.
UNIX is a multi-user, multitasking operating system that offers virtual memory and time sharing capabilities on computers ranging from PCs to mainframes.

61. Utility Programs
A utility program assists the user in maintaining and improving the efficiency of a computer system.
Some of the functions they perform include:
File handling (backup/recovery, delete, rename, sort/merge, copy, etc.)
Data compression
Text editing
Virus protection