1. Introduction to Computers

2. What is software?
A set of instructions that tell a computer how to perform a specific task
Written in one of many computer languages
The instructions must follow a set of rules called syntax just as English must follow rules of grammar
Syntax is governed by the computer language used
Usually consists of many elements including instructions, forms, icons, help text, etc.
Not a physical thing, you can’t touch software

3. Elements of software Consists of many types of files working together:
Programs (.exe) –a main executable file
Shared modules (.dll) –executable file supporting the main executable & shared by multiple programs
Data files (.dat and others) –contains data needed by the program(s)
Text files (.hlp & .txt) –information for users
Graphics files (.ico, gif, pcx, and others) – contains graphics used such as icons and other images
Plus other types of files too numerous to mention

4. A program is installed in a folder
Note the various files required for this particular program
Programs
Shared Modules
Data File
Images
Icons
Sound Files

5. Programming is highly detailed
Software provides a task-related environment
Word displays the document the user creates
Excel displays rows and columns of a spreadsheet
Internet Explorer displays web pages
A programmer defines the entire environment including every icon, text box, button, and menu
Must define height, width, location, and other characteristics of each element in the environment
And more importantly, the actions to perform when the user clicks on an element in the environment

6. A program – Convert Farenheit to Celsius
txtFarenheit
txtFarenheit Characteristics
Private Sub btnConvert_Click
'Declare working variables needed
Dim farenheit As Single
Dim celsius As Single
'Make sure text box contains a number
If IsNumeric(txtFarenheit.Text) Then
'Convert text box entry to a number
farenheit = Val(txtFarenheit.Text)
'Calculate the equivalent Celsius temperature
celsius = (farenheit - 32) * 5 / 9
'Place resulting celsius temp in the form
lblCelsius.Text = celsius.ToString
Else
'If no number in text box, display error message
MessageBox.Show("Please enter a number to convert")
End If
End Sub
lblCelsius
btnConvert

7. High-level languages
Previous slide an illustration of the Visual Basic programming language
Visual Basic is a high-level language
Most software is written in a high-level language
Allows programmers to create complex instructions well above the level at which the processor operates
A set of instructions in a high-level language is referred to as source code
Other high-level languages include C, C++, Java, Fortran, and COBOL

8. Machine Language
The processor executes instructions at a fairly simple level called machine language
Processor dictates the machine language used
High-level Language Instruction
Equivalent Instructions In
Machine Language
Description of Machine Language Instruction
Answer = Number1 + Number2
Move RAM Location Called Number1 into Register 1
Move RAM Location Called Number2 into Register 2
Add Register 1 and Register 2 to the Accumulator
Move Accumulator to RAM Location Called Answer

9. The role of a compiler A Visual Basic program has a .vb extension
Must translate high-level language source code to the 1s and 0s of machine language
A compiler does this conversion, creating a .exe program file called object code
Program is then run by executing the .exe file

10. Interpreters
Some high-level languages use an interpreter instead of a compiler
An interpreter does not create a .exe file
Instead it converts high level language instructions to machine language one instruction at a time
Resulting machine language instructions are immediately sent to the processor for execution
Machine language instructions are not saved
Program must be re-interpreted every time it’s run

11. Interpreters versus compilers
Interpreters are simpler
Convert to machine language & send to processor
But the interpreter is needed on every machine that must run an interpreted program
Compilers are more efficient
Conversion to machine language happens one time
Program can execute repeatedly with no re-compile
Compiler required on programmer’s computer only
No compiler needed when executing the program

12. Platform dependence
Machine language programs must utilize the instruction set of the processor they will run on
It’s why processor is a determining factor in compatibility between computers
A compiler creates a machine language program intended for a particular family type of processor
The same high-level language may be used on multiple platforms
But the compiler must be changed to produce object code compatible with that platform

13. Software categories
System software performs tasks dealing with the internal operations of the computer
Provides a reliable platform for application software
Includes the operating system, device drivers, utilities, and programming languages
Application software performs tasks needed by a user
Includes many types such as document production, spreadsheets, database, music, accounting, etc.