Introduction to DOS

DOS
Microsoft Disk Operating System is the Microsoft-marketedversion of the first widely-installed operating system in personal computers.
It was essentially the same Operating System that Bill Gates'syoung company developed for IBM as Personal Computer- Disk Operating System(PC-DOS).
Most users... of either DOS system reffered to their systems asDisk Operating System .
Like PC-DOS , MS-DOS was (and still is) a non-graphical line-oriented command driven operating system, with a relatively simple interface but not overly "fiendly"user interface.Its prompt to enter a command look like this :
C:>
The first Microsoft Windows operating system was really an application that ran on top of MS-DOS operating System.
Today, Windows operating Systems continue to support DOS(or a DOS-like user interface) for special purpose by emulating the operating system.
Introduction to Operating System   Introduction   Most Personal Computers run under the MSDOS Operating System. MSDOS being the Microsoft Disk Operating System. It is estimated that almost 10 million machines run under the MSDOS Operating System and some 20,000 or more end-user applications have been published to run with it.     The Operating System is the program which provides organized services to the computer user and the application programs that they wish to use. These services consist mainly of access to the hardware resources such as the disk drives, keyboard, etc.   The Operating System has three main constituents:- 1. The system files which are hidden. Their function is to perform such basic tasks as reading the keyboard, displaying characters on the screen, opening and closing files etc.   2. The command interrupter, COMMAND.COM which reads commands typed at the keyboard and attempts to obey them. COMMAND.COM has some simple commands built in - these are known as internal commands.   3. A series of utility programs covering functions not handled by the internal commands. There are approximately 52 of these commands; the exact number varies between different versions of MSDOS, ranging from COPY to copy files to EDIT the text editor, and many more.     Therefore, the Operating systems provide a software platform on top of which other programs, called application programs, can run.   The application programs must be written to run on top of a particular operating system. Our choice of operating system, therefore, determines to a great extent the applications we can run. For PCs, the most popular operating systems are DOS, OS/2, and Windows, but others are available, such as Linux.         Introduction to Operating System   Disks and Drives   Because most of our computers Memory (RAM) is temporary, its contents are erased when we switch off the power. We need a place to store the Operating System, application programs and our work. That's where disks come in, we store any information you want to keep onto disks.   There are two types of disk: 1. Floppy disks & 2. Hard disks.     1. Floppy disks (Diskettes) A disk is a magnetically coated disk of thin plastic, inside a rigid plastic cover.   We can use Floppy disks to: • Transfer information from one computer to another. • Store the Operating System, or application program and our work, if we don't have a Hard disk. • Keep a copy of information that we have on our Hard disk (Backup).   We need only format a disk once. After that, we can use the disk again and again without having to reformat it. Formatting a disk we have previously used erases any data on the disk, so only reformat a disk if we are sure we don't need any of the data on it.     Choosing disks Diskettes come in various forms, so it is important to choose diskettes that match the type of diskette drive installed in our computer.   Several different types are available: • 5.25inch 360 Kbytes - Very rarely used now • 5.25inch 1.2 Mbytes - Uncommon but still in use • 3.5inch 720 Kbytes - Getting less common, still in use • 3.5inch 1.44 Mbytes - The standard in most modern computers.     It should be noted that:- • A 720 Kbytes drive can only read and write to a 720 Kbytes diskette • A 1.44 Mbyte drive can read and write to both 720 Kbytes and 1.44 Mbyte diskettes. However we must use special formatting instructions to format a 720 Kbytes diskette in a 1.44 Mbyte drive. • The visible difference between a 720 Kbytes diskette and a 1.44 Mbyte diskette is that there is no extra notch on a 720 Kbytes diskette.     2. Hard disks A Hard disk is a disk that is enclosed in a permanently sealed metal housing.   Hard disks are better than Floppy diskettes in two main respects: • We can store much more information on a Hard disk than on a diskette. For example, a 40 Mbyte Hard disk holds the equivalent of almost twenty nine 1.44 Mbyte Floppy diskettes.   • They are up to 600 times faster at finding and loading information into the computers Memory.         Introduction to Operating System   Working with Files and Directories   The most fundamental aspects of using computer – 1. working with files, and 2. Organizing those files into directories.     Files A file is simply a collection of information that we store on a disk or diskette. The normal way to create a file is to run an application. For example, when we use a word processing application to write a letter, we save the letter by storing it as a file.   In general, each file must have a unique name. However, two files can share the same name provided that they are on different disks, or in different directories.   A file name has two parts: • the filename itself and • an extension.   In this example: RECIPE.DOC RECIPE is the filename and DOC is the extension. Note the FULL STOP between the two parts of the name. When a filename has an extension, the two parts of the name are separated by a full stop.     Filenames We choose filenames with care, as a good name will help us to remember what kind of information is in the file. A filename may contain up to eight characters.   For example: PDL, README, 4JULY96, MEMO_MAY     Exceptions The only characters we cannot use in filenames are: " / \ [ ] < > + = ; : , ? * { } Spaces are also not permitted. Some filenames to avoid   There are some filenames that we should avoid when naming files because our computer reserves them for special uses.   AUX, COM1 or COM2 The internal name of a device connected to a Serial Port.   CON The internal name of data sent to the keyboard or screen.   LPT1, LPT2, LST or PRN The internal names for the printer connected to the Parallel port.     Extensions We use extensions to make our filenames more descriptive. For example we could add the extension DOC to every document we write. Then when displaying a list of the files on our disk, we can tell quickly which files contain documents.   NOTE:- Some applications add their own unique extensions, these should NOT be altered. If we do the program may not be able to use them. An extension may contain up to three characters.   These are all valid extensions: A , TXT, 88, B_2     Taking care with extensions There are some extensions to which our computer attaches a special meaning. Only add these extensions to a file if we are sure the file performs the correct function:   BAK A backup file. When we save a file, the previous version of that file MAY be automatically saved as a backup with a BAK extension.   COM or EXE A program or MSDOS /application file   $$$ An incorrect or compressed file.     Directories One way of organising the files on our computers Hard disk is to put them in different directories. Directories enable us to arrange our files in whatever way we want and get files we need quickly. Every disk has one basic directory, called the ROOT directory, which we create automatically when we format the disk. As well as putting files in this directory, we can also create directories inside it. Each subdirectory can hold files, and in turn, further subdirectories. The number of subdirectories on a disk is limited only by the amount of storage space on the disk.   We can visualise a system of directories as an upside-down tree, with the root directory at the top and the subdirectories branching off it.     Pathnames If we use directories, we must tell our computer where to look for any particular file we want to edit. We do this by specifying the pathname of the file. A pathname is a sequence of directory names followed by a filename. Each directory name is separated from the previous one by a backslash ( \ ).   For example the pathname for a file called MEMO.DOC could be :- C:\USER\PETER\MEMO.DOC