1 Application & Systems Software Operating Systems – a deeper look

2 Included in today’s work: Follow up Lecture What is an Operating System (OS)? A quick look at Operating Systems Some finer points of MS-DOS Files and Directories Extending the command set

3 What are Operating Systems? They define our computing experience. First software we see when we turn a computer on. ‘Enables’ all the programs we use. Organises and controls all the hardware. Hides the details of all the actual processing from the user.

4 Some Examples Not all computers have operating systems. All desktop computers have an OS: –Windows family (95, 98, 2000, NT); –UNIX family (Linux, BSD, UNIX, etc); –Macintosh OS; Hundreds of others: –Mainframes, robotics, manufacturing, etc.

5 So what does an OS do? Manages the hardware and software resources of the computer system: –e.g. processor, memory, disk space. Provides a stable, consistent way for applications to deal with the hardware without having to know all the details of the hardware.

6 Various programs and input methods compete for the attention of the CPU and demand memory, storage and input/output (I/O) bandwidth for their own purposes. The OS acts like a “good parent”, making sure that each application gets the necessary resources, ensuring that the limited capacity of the system is shared out for the greatest good of all users and applications.

7 The provision of an consistent application interface is very important when there is more than one type of computer using the OS. Windows 98, for example, runs on hardware from thousands of vendors and accommodates thousands of different printers, disk drives and special peripherals.

8 Basic Functions of OS Wake-Up Call –The first program that runs is usually a set of instructions kept in the computers ROM. This examines the system hardware to make sure everything is functioning properly –This is the Power-On Self Test (POST) –After POST, the software loaded in ROM will begin to activate the computer’s disk drives. –In most modern computers, the first bit of OS loaded is the bootstrap loader.

9 Bootstrap Loader 1 single function –Loads the OS into memory and allows it to begin operation Sets up the small driver programs that interface with and control the various hardware sub-systems of the computer. Divides the memory into those bits that hold the OS, user information and applications. Finally turns control of the computer over to the OS

10 OS Tasks Falls into 6 general categories –Processor management –Memory management –Device management –Storage management –Application interface –User interface

11 Processor management Managing the processor concerns two issues: ensuring that each process & application receives enough CPU time maximising the number of CPU cycles used for real work The OS controls and schedules processes. It handles interrupts, and prioritises tasks

12 Memory Management Two tasks are performed: the OS works out how much memory to allocate to a particular process the OS decides which type of memory in the system can be used for which part of each process The crucial factor here is the different types of memory and their speeds.

13 Device Management Each peripheral requires a driver This is a special program to translate between the hardware and high-level programming languages. Part of the OS function is to communicate with these drivers and to assign priorities to data and commands going to and coming from the device.

14 Storage management Drivers are also used to manage memory storage peripherals e.g. disks, tape etc. One function of the OS is to configure and manage part of the storage device for virtual memory. A further function of the OS is to determine which parts of “current processes” are consigned to this virtual memory. A third function is that of file manager, to keep track of and to recall all the files and programs stored in the device.

15 Application interface An Application Program Interface (API) allows Application programmers to use and program various functions of the computer and OS without needing to know all the details of the CPU operations. Such an API may, for example allow a programmer access to disk storage and to read mouse commands, without having to worry about the different kinds of disks and mice which might be used.

16 User Interface The UI provides a consistent way for the user to interact with the computer, which is common to all models and manufacturers There are two main types of UI: –Graphical User Interface (eg Windows) –Command Line Interface (e.g MS-DOS) Other Operating Systems may deliver a mixture of these two.

17 Finding out more about Operating Systems The information presented here is an introduction to a very extensive subject. You should follow up some of these ideas by: –Reading the IMC booklets –Attending the lectures –Checking out: system.htm system.htm

18 A brief overview of MS-DOS When you activate the Command Prompt, a new window should open (called command prompt) and it will probably contain something like: –Microsoft Windows 2000 [version ] (C) Copyright Microsoft Corp. C:\>

19 DOS Conventions All DOS commands are activated by typing the commands and pressing the key. DOS is not case-sensitive. Spaces are the primary separators in DOS commands. One or more spaces must follow each command word, and file names are delimited by spaces – therefore, files names may not contain spaces.

20 The DOS Prompt e.g. C:\WINDOWS\SYSTEM> C: the default disk drive \ the root directory WINDOWS\ name of a subdirectory in the root SYSTEM\ name of a directory in the WINDOWS subdirectory >Ready for your command

21 DOS Disk Concepts Each disk drive is assigned a letter A colon after the drive letter identifies it as a drive name, as opposed to a file name The letter is associated with the drive, not the disk. Certain letters –A: = floppy disk –C: = primary hard disk drive

22 Changing Drives If your screen cursor is at: C:\> Type in C:\> A: (and press return) The screen cursor changes to A:\> The system has changed drives. Previously we were “looking at” the hard drive C:, now we are looking at the floppy disk A:

23 Listing a Directory Command –dir This command is an instruction to DOS to list the directory for the folder which you have selected. DOS remembers the “position” that you are in the directory structure. This is called the “default”.

24 DOS File Concepts Files on the disk are named things like se3.doc, notes.ppt and go.exe etc. A filename potentially has two parts to it: –the filename (up to 8 letters) –the extension (up to three letters) The “.” is merely a separator, used to keep the two elements apart, so that DOS can find files of a particular type.

25 Directories, Subdirectories If you look in any folder you will see a collection of files and folders Listing the Directory will tell you what is in there. A subdirectory is merely a list of what is in any of the folders within the current directory.

26 DOS Directory Concepts Files are collected together in folders –so for example a folder called semester4 might contain the documents week1.doc, week2.doc etc. Semester 4 week1.docweek2.docweek3.doc

27 DOS Directory Concepts groups of folders can be put into other folders, –so for example a folder called year2 might contain the folders semester1 and semester2 Year 2 Semester3Semester4 week1.docweek2.docweek3.doc

28 DOS Directory Concepts This process of putting files into folders and folders into other folders continues up to the level of the root directory, the disk drive’s main folder. C:\ IMCBACE Year 2ProgramsGames

29 Example Directory Structure

30 Changing Drives/Directories Make C: the default –c: Make the root default –cd\ Change to winword directory –cd \msoffice\winword Change to the parent directory (one up) –cd..

31 Creating Directories To create a new directory, we can type in: MD sysenv This will create a new subdirectory called sysenv within the current directory at the present location in the directory structure.

32 Other Directory Commands Other Commands: To put the listing across the screen (Wide) –dir /w To order the listing by name –dir /o To include subdirectories –dir /s

33 Removing directories To remove a directory, we can type in: RD sysenv This will remove the subdirectory called sysenv within the current directory at the present location in the directory structure. Note that this will only work if the directory is empty.

34 Interpreting a Directory Listing Volume in drive A is MINI_BOOT Volume Serial Number is E9 Directory of A:\ COMMANDCOM :00a DEFRAGEXE :00a DEFRAGHLP :00a 3 file(s) bytes bytes free

35 Interpreting a Directory Listing Volume in drive A is MINI_BOOT –Volume label can be given when formatting a disk, or by using the label command Volume Serial Number is E9 –Serial number is assigned automatically when formatting.

36 Interpreting a Directory Listing Directory of A:\ –This disk is in A: drive, and we’re looking at the “root” directory COMMAND COM :00a –A file called command.com, which occupies 52,925 bytes and was last modified at 6 am

37 Interpreting a Directory Listing 3 file(s) bytes –There are three files occupying a total of 137,185 bytes in this directory bytes free –You could store another 1,188,352 bytes on this disk

38 Date and Time There is a system clock, which keeps the time even when the power off. The commands TIME and DATE allow you to reset the clock. DATE Current date is Mon Enter new date (dd-mm-yy): This allows you to set a new date (e.g )

39 Looking at Files The TYPE command allows you to inspect the contents of files. TYPE students.txt Displays the contents of the text file called students.

40 Deleting, Renaming & Copying Del file1 This removes a file in the current directory with the name specified by file1 Del oldfile.doc

41 Deleting, Renaming & Copying Rename file1 file2 (Note spaces) Changes the name of a file in the current directory from file1 to file2 Rename oldname.ppt newname.ppt

42 Deleting, Renaming & Copying Copy file1 file2 (Note spaces) This copies the file at the name and location location specified by file1 to a file at the name and location specified by file2 Copy C:\sysenv\dos.txt A:\lect1.txt

43 Deleting, Renaming & Copying Copy from default to a:\ –Copy file.ext a:\ Copy from a:\ to default –Copy a:\file.ext Delete one file –Del a:\file.ext Rename a file.abc to file.xyz –Rename file.abc file.xyz

44 Using Wildcard Characters A Wildcard Character allows you to type in a name without specifying it completely. This means that you can work on all files of a particular type For example, suppose that you wished to find all word files. These have the extension DOC, so you would use specify *.DOC as the filename. The * is a wildcard.

45 Using Wildcard Characters Matching any group of letters –* (star or asterisk) matches any group of letters in the file name after the asterisk Matching any single letter –? (question mark) matches any single letter in the file name.

46 Listing a Directory using wildcards List all files –dir *.* All files with same extension –dir *.ext All files with a particular name, regardless of their extension –dir name.* All files within a specific directory –dir c:\web\site\*.*

47 Creative use of Wildcards dir q*.* –List all files beginning with the letter q copy *.bat b: –Copy all files with the extension bat to drive b: dir budget?a.dat –List files whose name begins with budget, has any single character, ends with a and has the extension dat.

48 Finding out more about DOS Links to help you with DOS Commands MS-DOS Survival Guide q02cd.htmhttp://courses.wccnet.edu/computer/mod/ q02cd.htm EasyDOS Command Index DOS 7 Full Command list