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DISK OPERATING SYSTEM (DOS)Operating SystemDefinition:Sometimes abbreviated as "OS, an operating system is the program that, after being initially loaded into the computer by a boot program, manages all the other programs in a computer.

The other programs are called applications or application programs. 2Operating SystemDefinition (continuation):The application programs make use of the operating system by making requests for services through a defined application program interface (API).

In addition, users can interact directly with the operating system through a user interface such as a command language or a graphical user interface (GUI).(Application Programming Interface) A language and message format used by an application program to communicate with the operating system or some other control program such as a database management system (DBMS) or communications protocol. APIs are implemented by writing function calls in the program, which provide the linkage to the required subroutine for execution. Thus, an API implies that a driver or program module is available in the computer to perform the operation or that software must be linked into the existing program to perform the tasks.3Operating SystemFunctions:Allocating and assigning system resourcesScheduling operationsMonitoring system activitiesStandard means of communication between user and computer4Operating SystemExamples of Operating Systems: DOS - Disk Operating System one of the first operating systems for the personal computer. When you turned the computer on all you saw was the command prompt which looked like c:\ >. You had to type all commands at the command prompt which might look like c:\>wp\wp.exe. This is called a command-line interface.

5Operating SystemExamples of Operating Systems:Windows A product of Microsoft, it is a GUI (graphical user interface) operating system. This type of "user friendly" operating system is said to have WIMP features:WindowsIconsMenusPointing device (mouse)6Operating SystemExamples of Operating Systems:MacOS - Macintosh a product of Apple, has its own operating system with a GUI and WIMP features.Unix - Linux (the PC version of Unix) Unix and Linux were originally created with a command-line interface, but recently have added GUI enhancements.7Disk Operating SystemIt was the first widely-installed operating system for personal computers. Earlier, the same name had been used for an IBM operating system for a line of business computers.The first personal computer version of DOS, called PC-DOS, was developed for IBM by Bill Gates and his new Microsoft Corporation. He retained the rights to market a Microsoft version, called MS-DOS. 8Disk Operating SystemPC-DOS and MS-DOS are almost identical and most users have referred to either of them as just "DOS.DOS was (and still is) a non-graphical line-oriented command- or menu-driven operating system, with a relatively simple interface but not overly "friendly" user interface. Its prompt to enter a command looks like this:C:>

The first Microsoft Windows operating system was really an application that ran on top of the MS-DOS operating system. Today, Windows operating systems continue to support DOS (or a DOS-like user interface) for special purposes by emulating the operating system.In the 1970s before the personal computer was invented, IBM had a different and unrelated DOS (Disk Operating System) that ran on smaller business computers. It was replaced by IBM's VSE operating system.

9Disk Operating SystemDOS PromptThe message DOS displays when it is ready to accept input on the command line.The default DOS prompt (C:\>, D:\>, etc.) displays the current drive and directory. 10Disk Operating SystemTypes of DOS Commands:Internal CommandsThese commands do not require any special files for being executed and are brought into the computer's memory as soon as the computer is switched on.

Examples: COPY, DEL, DIR, TYPE, CD, MD, CLS, DATE, TIME and PATH. 11Disk Operating SystemTypes of DOS Commands:External CommandsThese commands require certain special DOS files to get executed.

Examples: FORMAT, CHKDSK, XCOPY, PRINT, ATIRIB, DISKCOPY, etc. You may not necessarily have all these files in your system. While copying these files onto your system, you must take care that they are of the same DOS version which is installed in your system. Otherwise, you may face problems. For instance, messages like, Incorrect version may appear on your screen if the DOS version is different from the copied file version.

12Disk Operating SystemBasic DOS Commands:CLS (internal)Clears the screen.DATE (internal)View or change the systems date.TIME (internal)View or modify the system time.VER (internal)Displays the version information.13Disk Operating SystemBasic DOS Commands:DIR (internal)List the contents of one or more directory.

14Disk Operating SystemFile NameThe name of a file.Example:EXER1.DOC

File Name Base Name Extension (8 char) (3 char)

15Disk Operating SystemConsiderations in giving a file a name:A file name can contain a number but it cannot start with a number.A file name cannot contain white spaces; the underscore can be used instead to separate characters.Give a file a name that would tell you about the contents of the file.

16Disk Operating SystemFile Manipulation Commands:COPY (internal)Copy one or more files to an alternate location.Format: COPY RENAME/REN (internal)Renames a file or directory.Format: RENAME 17Disk Operating SystemFile Manipulation Commands:DEL (internal)Deletes one or more files.Format: DEL TYPE (internal)Display the contents of a file.Format: TYPE 18Disk Operating SystemDirectory Commands:MD/MKDIR (internal)Command to create a new directory.Format: MD CD/CHDIR (internal)Changes directories.Format: CD 19Disk Operating SystemDirectory Commands:RD/RMDIR(internal)Removes an empty directory.Format: RD

Conditions to be satisfied before a directory can be removed:The directory to be removed must be empty.The directory to be removed must not be the current directory.20Directory TreeABCFDEIGHKJ21