Thursday, September 18, 2014

How is DOS used?

How is DOS used?

When you type anything at the DOS prompt, and press enter, you are telling DOS to run a program.
It will first look to see if there is an internal command program which has that name, and if it does not find one, then it will look to see if there is a file on disk with that name.


If it finds an external file with the extension .COM (command), or .EXE (executable), then the program is loaded and run. At this point DOS looses control of the computer until the program has ended. However, parts of it are still used by the programs as they are running, eg to load and save files etc.

How are directories named?

Every disk drive has a root directory which can have sub-directories which are named in the same format as file names, (though generally without any extension). The sub-directories can have sub-directories and so on. Eg: a floppy disk might contain the following directory structure:


PICTURES

HOLIDAYS

ITALY

FRANCE

FAMILY

PETS

TEXT

LETTERS

EMAIL


A directory path name includes the disk drive and all sub-directories needed to specify a directory on a disk. The disk drive is specified by a single letter. Eg: The floppy disk drive is A and the hard disk drive is C.


The drive letter, is followed by a colon, the directory path names are separated by backward slashes (\), (*Not* forward slashes like internet addresses). Eg. In the above example:


“A:\PICTURES\HOLIDAY\FRANCE” would be more than likely to contain pictures of a few baguettes and onions.

How are files named?

While newer versions of DOS support longer file names, the standard DOS filename format remains: 1-8 letter name, period, 3 letter extension eg:

PROGRAM.EXE

DATA.DAT

LETTER.DOC


The extension to a file’s name is there to allow files of a similar type to be grouped together. i.e. all word processor files might have the extension .DOC, while all picture files might have the extension .pic While these extension can be specified by the user, many programs have used them to differentiate between formats, and so they have gradually become standardized. For example you would expect a “.TXT” file to be a file containing un-formatted text, or a “.BMP” file to be in a bit mapped graphics file format.


To completely specify a file on your computer you must specify its drive and directory path, and its file name. However a file does not always have to be specified in this complete form: If it is in the current directory, then you can just enter its file name.

How does DOS organize disks?

DOS works within a file, directory and disk drive structure. This means that all program and data files are names, and grouped together in named directories on disks. ‘Directories’ are just lists of files.

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