Operating Systems

1. Operating Systems Components

2. Operating System Components • An operating system is conceptually broken into three sets of components: • a user interface (which may consist of a graphical user interface and/or a command line interpreter or "shell"), • low-level system utilities, • a kernel - which is the heart of the operating system.

3. What is a kernel • The central module of an operating system. • A piece of software responsible for providing secure access to the computer hardware. • A kernel includes • an interrupt handler that handles all requests or completed I/O operations that compete for the kernel's service. • a scheduler that determines which programs share the kernel's processing time in what order. • a supervisor that actually gives use of the computer to each process when it is scheduled.

4. Types of kernels • Monolithic Kernel • includes all (or at least, most) of its services in the kernel proper. • the amount of code running in kernel space makes the kernel more prone to fatal bugs. • Linux uses a monolithic kernels that allows loading and unloading of kernel modules at runtime. • Microkernel • runs most services - like networking, filesystem, etc. - in user space. • microkernels can be more stable, but require additional design work.

5. Types of kernels • Hybrid (Modified Microkernel) • microkernels that have some "non-essential" code in kernelspace in order for that code to run more quickly. • Windows NT/2000 and Macintosh OS X use hybrid kernels

6. User Interface • The user interface is a program or set of programs that sits as a layer above the operating system itself. • Two common types of user interfaces: • Text-based also called command-line interfaces. • Graphical

7. Command-Line Interface (CLI) • Method of interacting with a computer by giving it lines of textual commands either from the keyboard or from a script. • In its simplest form the user types a command after the computer displays a prompt character. • Programs that implement these interfaces are called command-line interpreters.

8. Advantages of CLIs • Skilled users may be able to user a command line faster than a GUI for simple tasks. • All options and operations are invokable in a consistent form, one "level" away from the basic command. • All options and operations are controlled in more or less the same way. • Can perform operations in a batch processing mode without user interaction.

9. The Windows XP Command-Line Interface

10. Windows Command Prompt Commands • Windows uses a program called CMD.EXE to interpret user commands. • Command Format • command-name options argument • only the command-name is mandatory • the options component consists of one or more switches flagged by an initial forward-slash (/) character. • Batch files • Group of commands in a file that run one after the other. • Uses a very simple control language – IF, FOR, GOTO. • Has a .CMD or .BAT extension.

11. Examples of Windows Commands • HELP – displays list of available commands • DEL FILE1.TXT – deletes a file named FILE1.TXT in the current folder. • COPY \MYSTUFF\FILE2.DOC FILE3.DOC – copy FILE1.DOC in the MYSTUFF folder to FILE3.DOC in the current folder • DIR /OD – displays list of files in current folder sorted by date, oldest first • DIR /X /P – displays list of short names of files in current folder, pausing after each screenful. • XCOPY /S *.TXT \MYSTUFF – copies all files with the .TXT extension in the current folder and all sub-folders into the MYSTUFF folder.

12. Example of a Windows Batch file REM This batch file will append a .BAK extension REM to all .TXT files in the current directory REM Commands will not be echoed @ECHO OFF REM %1 is a positional parameter, REM in this case it refers to the first character after REM the batch file name REM Example of an IF-statement IF %1==N ECHO Skipping

13. Windows Batch File continued REM Example of a GOTO GOTO L%1 REM This is a label :LY DIR /B *.TXT REM Example of a FOR-loop FOR %%F IN (*.TXT) DO REN %%F %%F.BAK DIR /B *.BAK :LN ECHO All Done

14. Windows Scripting Host (WSH) • A Windows administration tool that extends the scripting functionality beyond batch files. • Creates an environment for hosting scripts. • Scripts can be run from either the Windows desktop (double-click on the file) or the command prompt (CSCRIPT <filename>). • Scripts can be written in VBScript (.VBS) or JavaScript (.JS). • Built into Microsoft Windows 98, 2000, and XP.

15. A Simple WSH Script REM The Famous HELLO WORLD Program WSCRIPT.ECHO “Hello World”

16. A More Complex WSH Script REM This script will copy all files whose names REM contain .txt to a sub-directory, the name REM of the sub-directory will be the current date REM in YYYYMMDD format REM Declare some variables DIM fs, today

17. WSH Script Example continued REM This is an example of a function REM This function will output a string REM zero-filled to the left up to a specified length FUNCTION zero_pad(p_in, p_length) IF LEN(CSTR(p_in)) >= p_length THEN zero_pad = CSTR(p_in) ELSE zero_pad = STRING(p_length - LEN(CSTR(p_in)), "0") _ & CSTR(p_in) END IF END FUNCTION

18. WSH Script Example continued REM Create a file system object which allows manipulation REM of files and folders set fs = WSCRIPT.CREATEOBJECT("Scripting.FileSystemObject") REM Build the sub-directory name today = CSTR(YEAR(DATE())) & zero_pad(MONTH(DATE()),2) _ & zero_pad(DAY(DATE()),2) REM Create the sub-folder if it does not already exist IF NOT fs.FOLDEREXISTS(today) then fs.CREATEFOLDER(today) REM Copy files to the sub-folder REM over-write if they already exist fs.COPYFILE "*.txt.*", today & "\", TRUE

19. UNIX Command System • A program called a shell is used to interpret UNIX commands. • UNIX has numerous shells – Bourne Shell, C-Shell, Bourne-Again shell, etc. • UNIX commands are case-sensitive • Command Format • command-name options argument #comment • only the command-name is mandatory • the options component consists of one or more switches • each switch consists of a minus-sign followed by one or more characters. • Scripts • group of commands in a file that run one after the other. • UNIX has a very powerful control language, comparable to other programming systems.

20. Examples of UNIX Commands • pwd – displays names of current directory. • ls -l /tmp – list files in /tmp in long format. • rm -r * – delete all files in current directory and all sub-directories • cp /tmp/*sh /home/class – copy all files in the /tmp directory whose names in sh to the /home/class directory • mkdir new1 – create a sub-directory called new1 in the current directory

21. A Simple Unix Shell Script #! /bin/sh # The preceding line indicates that this is a # Bourne-shell script # This shell script will create sub-directories # in the current directory with names new1 to new9 for d in 1 2 3 4 5 6 7 8 9 do # The $d indicates that the value of variable d is substituted mkdir new$d done

22. Graphical User Interface (GUI) • First GUI developed at the Palo ALTO Research Center of Xerox Corporation. • Apple Macintosh, released in 1984, was the first commercial use of a GUI. • GUIs have a number of common features: • on-screen overlapping windows • pointing device • graphical features, such as buttons, icons, etc. • higher level devices, such as menus, toolbars, etc.

23. Features of a GUI • Window – main central area used to display and interact with user data. • Scroll bar – used to reposition the viewing window. • Title bar – indicates the name of the program currently being used and its associated document. • Menu bar – list of words which constitute the top-level choices of a menu. • Pop-up/Drop-down menu – list of choices that appear when a top-level menu item is clicked. • Toolbar – Group of icons that perform a function when clicked.

24. Some examples oftoolbars Microsoft Word MicrosoftExcel MicrosoftAccess Note the use of icons that are common to all the toolbars Fast Save, Print, and Print Preview Examplesinclude: Help

25. Someexamplesof drop-down menus Note that options that are not available are ‘greyed’ or ‘ghosted’

26. Some examples of pop-upmenus The Microsoft Windows ‘Start’ Menu pops up when the ‘Start’ button is pressed The ‘AutoShapes’ Menu in Microsoft Word pops up when the ‘AutoShapes’ button is pressed

27. Advantages of GUIs • Performing tasks in a GUI environment is intuitive. • Applications have the same general appearance and operation. • Applications are flexible, commands can be executed using either mouse or keyboard. • GUIs allow you to cancel or undo operations. • GUIs often ask you to confirm important operations.