1. SIMS-201
Computer Software

2. Overview Computer Software Assembly Code Operating System
Programming Language
Application

3. Introduction
Computer software consists of the instructions and application programs that permit computers to accomplish tasks
It is called software because, unlike hardware that has fixed configurations, connections, and operation, the software is flexible and easily modified
Software programs control computers at 4 different levels:
Assembly code
Operating system
Programming language
Application

4. Hierarchy of Software Application Operating System Assembly Code
Programming Language
(High Level Language)
Application

5. Assembly Code
Assembly Code, also called assembly language is the most basic language of the computer and consists of elementary instructions recognized by the CPU
It is a a human-readable notation for the lowest level language-the machine language that a specific computer architecture uses. Machine language, a mere pattern of bits, are instructions directly recognized by the CPU
Machine language is made readable (i.e. converted to assembly language) by replacing these pattern of bits with symbols called ‘mnemonics’ (ex. ADD, SUB, LOAD, JUMP)
Unlike high-level languages, there is a 1-to-1 mapping from simple assembly to machine language, so that computers can translate in both directions without losing information. Assembly language is converted to machine language by an assembler

6. Examples of assembly code instructions (mnemonics) include: ADD and MOV
Assembly code instructions perform the basic computer operations including moving data, changing contents of registers, adding the contents of two registers and jumping to different parts of a program
For example, the computer performs the arithmetic operation: as follows:
MOV 1, R0 (Move the number 1 into Register 0)
MOV 2, R1 (Move the number 2 into Register 1)
ADD R0, R1 (Add R0 to R1 and put the result in Register 1)
MOV 4, R0 (Move the number 4 into Register 0)
ADD R0, R1 (Add R0 to R1 and put the result into Register 1)
Assembly code is different for each type of computer and a code written for the Intel Pentium (IBM) microprocessor chip will not operate on the PowerPC (Macintosh) microprocessor

7. There are two types of instruction sets:
The set of instructions a processor recognizes (can execute) is called an instruction set.
There are two types of instruction sets:
Reduced Instruction Set Computer (RISC) – ex. AMD
Complex Instruction Set Computer (CISC) – ex. Pentium
The reduced instruction set only contains very simple instructions such as ADD, SUB (subtract), LD (load from memory) and is argued to be faster to execute. On the other hand, the complex instruction set includes the RISC + implements a few more complex instructions.

8. Operating System
The operating system is a set of commands that performs common system tasks such as accepting data from the keyboard, displaying data on the monitor, sending data to the printer, examining the contents of a directory, etc.
It is stored on the hard disk and is loaded to memory when the computer is switched on
An operating system is conceptually broken into two components: A shell and a kernel. The shell is a command interpreter and as the name implies, is an outer wrapper to the kernel which in turn talks directly to the hardware
Hardware Kernel Shell Applications
In some operating systems the shell and the kernel are completely separate entities, allowing you to run varying combinations of shell and kernel (eg Unix), in others, the separation is only conceptual (eg Windows).
Source: wikipedia.org

9. Examples of operating systems
MS-DOS (Microsoft disk operating system)
Introduced in 1981
Required basic familiarity with its operation and organization
Intel computers such as commonly used MS-DOS
Users were required to know basic commands (abbreviations) such as dir or del to perform tasks
Uses a command line user interface-is non graphical
MacOS
Introduced in 1984
Operating system for apple Macintosh computers
First commercially successful OS which used GUI (graphical user interface)
Used icons to represent data structures
Microsoft Windows
Often used with PC’s (home use)
Introduced in 1985 in response to MacOS

10. Unix and similar systems
MacOS X
Linux
Solaris operating environment
Microsoft Xenix
AIX by IBM

11. Linux Linux is causing a revolution in the world of computers
Initially created as a hobby by a young student called Linus Torvalds at the University of Helsinki in Finland
It may be used for a variety of purposes including networking and software development
It is often considered to be an excellent, low-cost alternative to other more expensive operating systems
The attractiveness of Linux is that its source code, which is a series of commands written in a programming language is freely available to anyone – open source
The source code can be modified to fit the individual needs of the user
It is developed under the GNU General Public License, enabling the user to share and change free software in comparison to most other software whose source code is concealed, preventing users to share or modify it
Source: linux.org

12. Operating system classification
Operating Systems can be classified as:
GUI: Graphical User Interface operating systems are operating systems that have the capability of using a mouse and are graphical
Multi user: allows multiple users to utilize the computer and run programs at the same time
Multi processing: allows multiple processors to be utilized
Multi tasking: allows multiple software processes (also called programs or applications) to be run at the same time
Multi threading: allows different parts (threads) of a software process to run concurrently

13. Programming Language
Higher level programming languages contain instructions that are more powerful, more general and better suited for programming a task than the basic assembly language instructions
Each higher level language instruction might consist of hundreds of assembly language instructions (after it is converted to assembly)
Software programmers write the most efficient and fastest programs in assembly language, however that is more difficult, error prone, and time consuming than using a higher level language
The higher level computer programming languages were invented to make program development easier. Examples of such languages are: FORTRAN, BASIC, PASCAL, etc.

14. Examples of programming languages:
Programs written by programmers are translated into the machine language by a compiler
Examples of programming languages:
BASIC
COBOL
Pascal C
C++
Java
C#.NET
Visual Basic
Perl
HTML
XML

15. Developing a Computer Program
Compiler
Link/load
Executable module
Source
code
Machine
language
Output
Input data
High-level
Low-level
Language
Programmer
Writes program in source code (higher level language)
Compiler
Converts source code to machine language code
Linker
Combines machine language with libraries & converts them to an executable module
Interpreter
Translates and executes one line at a time

16. How the program runs LDA 14 1 ADD 15 2 STA 14 3 HLT …. …… 14 10 15 7
Fetch-execute cycle
Main memory (RAM)
LDA 14 1
ADD 15 2
STA 14 3
HLT …. …… 14 10 15 7
Assume a is stored in 14
and b is stored in 15
Program
a= a + b
Result 14 17 15 7

17. Processes and Threads What is a process? What is a thread?
Executive
Executive
Per-process
address space
What is a process?
Represents an instance of a running program
You create a process to run a program
Starting an application creates a process
What is a thread?
An execution context within a process
All threads in a process share the same per-process address space
Thread
Thread
Thread
Systemwide
Address Space

18. Application programs
An application program is software written by a professional programmer for a specific operating system to perform a particular task such as word processing, spread sheet, graphic design, music editing, etc.
Before ‘shrink-wrap’ software was available, i.e. computer users also needed to be computer programmers who knew the operating system and at least one higher level language
Such knowledge is no longer necessary and software suitable for a particular application can be directly purchased
Examples of application software:
MS office
Netscape
Media player
MSN messenger
Adobe acrobat

19. Applications Numerical: (number crunching, arrays)
calculator, spreadsheet
weather forecasting, computer aided design
Symbolic: (data structures, translation)
compiler, interpreter,
scheduling, circuit layout
Information: (records, tables, disks)
database, accounts
World Wide Web, booking system
Systems: (devices, networks, control)
window/file/print managers
device drivers, network software

20. Application classifications
Classify based on how it was developed
Custom
Software applications that are developed within an organization for use by that organization
COTS
Commercial Off-the-shelf (COTS)
Software developed with the intention of selling the software in multiple copies
Custom software: organization has full control on specifications, functionality, ownership
COTS: generally no control
Software is sold, leased or licensed

21. Word processing and Electronic Spreadsheets
Create, edit, revise and print documents
E.g., Microsoft Word, Lotus WordPro and Corel WordPerfect
Electronic Spreadsheets
Worksheet of rows and columns
Used for calculations and charts
E.g., Lotus 1-2-3, Microsoft Excel, Corel QuattroPro

22. Desktop publishing and Presentation Graphics
Produce printed materials that look professionally published
E.g., Adobe PageMaker, Microsoft Publisher and QuarkXPress
Presentation Graphics
Convert numeric data into graphics displays
Prepare multimedia presentations including graphics, photos, animation, and video clips
E.g., Microsoft PowerPoint, Lotus Freelance, Corel Presentations, Keynote

23. Personal Information Manager and Groupware
Personal Information Manager (PIM)
Software for end user productivity and collaboration
Store information about clients, schedules, manage appointments, manage tasks
E.g., Lotus Organizer, Microsoft Outlook
Groupware
Software that helps workgroups collaborate on group assignments
discussion groups, videoconferencing, instant messaging
E.g., Lotus Notes, Novell GroupWise, Microsoft Exchange

24. Software Suites

25. Software Suites Software suites integrate application packages
Advantages:
Cost less than buying individual packages
All have a similar GUI
Work together well
Disadvantages
Features not used by all users
Take a lot of disk space

26. Web Browser
Application that supports navigation through the point-and-click resources of the Web
Browsing the web
Becoming universal for Internet-based applications
Internet Explorer, Netscape Navigator, Firefox, Safari

27. E-mail, Instant Messaging and Weblogs
Application to communicate by sending and receiving messages and attachments via the Internet, intranet or extranet
Instant messaging (IM)
Receive electronic messages instantly
Weblog or blog
Digital diary
Updated with new information about a subject or range of subjects

28. Software Licensing Software Applications are usually licensed
In other words, we purchase a license to use the application under the terms of a licensing agreement
This is done in order to protect the vendor’s intellectual property rights