1. Slide 6-1 Chapter 6 System Software Considerations Introduction to Information Systems Judith C. Simon

2. Slide 6-2 "Copyright © 2001 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in Section 117 of the 1976 United States Copyright Act without the express written permission of the copyright owner is unlawful. Request for further information should be addressed to the Permissions Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages, caused by the use of these programs or from the use of the information contained herein."

3. Slide 6-3 Chapter 6 Major Topics ä Purposes of system software ä Control programs ä Processing programs ä Language translators ä Utilities and other system programs ä Specific operating systems ä System software compatibility

4. Slide 6-4 What is System Software? ä Software that is designed to manage the computer resources, thereby reducing the need for human intervention.

5. Slide 6-5 General Purpose of System Software ApplicationSoftwareSystemSoftware

6. Slide 6-6 System Versus Application Software Application Software System Software System software typically is delivered on the hard drive with the purchase of a computer, although it can be acquired separately. Application software is usually added via floppy or optical disk or downloaded from a Web site.

7. Slide 6-7 Types System vs. Applications Software ä System Software ä Operating systems ä Control programs ä Processing programs ä Language translators ä Utility programs ä Applications Software ä Office support ä Management support ä Specialized activities

8. Slide 6-8 Purposes of System Software ä To communicate with the hardware as well as with application software ä To manage the resources of the computer by supplying programs that cause it to work properly and efficiently while performing operations such as input, processing, output, and storage activities of application software ä To reduce the need for human intervention, thus providing more productive systems

9. Slide 6-9 Purposes of Control Programs ä To handle the scheduling of computer activities ä To handle input/output activities ä To communicate with computer users through on- screen prompts and messages ä To determine the appropriate procedures when interruptions or other unusual events occur during execution of programs

10. Slide 6-10 Control Versus Processing Programs ä Control Programs ä Schedule computer activities ä Manage input and output tasks ä Provide communication link with computer users ä Processing Programs ä Manage the efficient execution of program instructions

11. Slide 6-11 Serial Processing ä Each program executed one instruction at a time, one program after another ä Not an efficient use of the computer’s processing power

12. Slide 6-12 Concurrent Processing ä Processor can move back and forth quickly from one task to another, thus appearing to be working on more than one task at a time; can manage more than one task “in progress” at a time, a concept often referred to as multitasking ä Some systems have preemptive multitasking, in which a priority system is used to determine which programs should be processed first ä Uses virtual memory, which gives the appearance of having unlimited memory by bringing in parts of programs at a time and quickly exchanging programs as needed, thus using the memory space more efficiently

13. Slide 6-13 Multitasking Example Task 1 - Report being printed Task 2 - Graph being printed Task 3 - Spreadsheet being developed System Software Managing One Processor Printer No. 1 Printer No. 2 Microcomputer

14. Slide 6-14 Simultaneous Processing ä Uses more than one processor so that multiple tasks or programs can be processed in the same moment in time; often called multiprocessing ä Front-end processor: use of one processor to coordinate I/O activities and to determine which activities should be performed by the other or larger processor(s); reduces demands on main processor ä Back-end processor: use of a separate processor for maintaining or housing a database; reduces demands on main processor

15. Slide 6-15 Multiprocessing - Several Tasks Task 1 Task 2 Task 3 Processor 1 Processor 2 Processor 3 Result 1 Result 2 Result 3 Several tasks on several processors

16. Slide 6-16 Multiprocessing: One Large Task Subdivided One large task subdivided

17. Slide 6-17 Language Translators ä Used to convert programming language statements (source code) into machine language (object code); machine language involves combinations of 1s and 0s; types include assembler, interpreter, compiler ä Assembler: used for assembly language, which was developed to be easier for programmers to write than machine language ä Interpreter: translates and executes each program statement individually and does not save the results ä Compiler: converts an entire program into machine language and saves the results for later use

18. Slide 6-18 Utilities and Other Programs ä Sometimes referred to as “housekeeping” programs because they often involve changing the appearance or location of data ä Examples include defragmentation and data recovery programs

19. Slide 6-19 Defragmentation and Data Recovery Programs ä Defragmentation: rearranging data into sequential clusters after they have become fragmented or scattered across a disk nonsequentially; this process increases access speed when locating a file ä Data recovery: locates clusters of a file that has been deleted from a disk if no other files have been stored; this process works because a file that you delete is actually just deleted from the file allocation table (FAT), which makes that space available for any new data that is stored

20. Slide 6-20 Operating Systems: Large Systems ä Operating system is designed for multiple users and is typically proprietary (developed for a specific large computer system). ä Example: MVS system used on large IBM systems

21. Slide 6-21 Operating Systems: Midrange Systems ä Operating system is typically designed for multiple users; some operating systems can be used on multiple types and sizes of computers. ä Example: UNIX-based operating systems

22. Slide 6-22 Operating Systems: Small Systems ä Operating system is designed for single users and can often be used on many brands of computers; predominant systems have been by Microsoft and Apple, with versions of UNIX becoming more widespread.

23. Slide 6-23 Small Computer Operating Systems MS-DOS Designed for IBM-compatible computers Mac OS Designed for Apple Macintosh computers Windows 3.1 GUI add-on for MS-DOS Windows 95/98 Designed more recently for IBM and compatibles Windows NT/ Designed for networked computers 2000 UNIX Designed originally for large systems, but versions by several developers now available for small systems

24. Slide 6-24 Software Compatibility ä Operating systems for one type of computer are not always compatible with other types of computers ä Trend is toward interoperability, where different operating systems can communicate with each other; a refinement of this concept is referred to as open systems, in which one system’s commands and data can travel to other systems without problems

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