The file system MS-DOS
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The file system
The DOS File system lets us store information in named files. You can call a file anything you like which might help you remember what it contains as long as you follow certain basic rules.
1. The names can be up to 8 characters long. You can use letters and digits but only a few punctuation marks (! $ % # ~ @ - () _ {}). You can't exceed 8 characters or use spaces or characters like * or ? or +. Names are case-insensitive, i.e. it doesn't matter whether you use capitals or lowercase letters; “A” and “a” are treated as the same thing.
2. File name can also have an extension of up to three characters, which describes the type of file. Three are some standard extensions, but you don't have to use them. Examples include COM and EXE for executable programs, TXT for files, BAK for backup copies of the files, or CPP for C++ program files. The extension is separated by a dot from the rest of the filename.
For example, a file called FILENAME.EXT has an 8 characters name (FILENAME) followed by a three- character extension (.EXT). You could also refer to it as filename.txt since case doesn't y, but I'm going to use names in capitals for emphasis throughout this document.
Files are stored in Directories; a directory is actually just a special type of file, which holds a list of the files within it. since a directory is a file, you can have directories within directories. Directory names also follow the same naming rules as other files, but although they can have an extension they aren't normally given one (just an 8-charecter name).
The system keeps track of your Current directory, and if you just refer to s file using a name like FILENAME.EXT it's assumed you mean a file of that name in the current directory. You can specify a Pathname to identify a file, which includes the directory name as well; the directory is separated from the rest of the name by a backslash (“\”). For example, a file called LETTER 1.TXT in a directory called SUVAM can be referred to as SUVAM\LETTER1.TXT (assuming that the current directory contains the SUVAM directory as a subdirectory). If SUVEM contains a subdirectory called PERSONAL, which in turn contains a file called SUVAM.TXT, you would refer to this file as SUVAM\PERSONAL\SRIRAM.TXT (i.e. look in the SUVAM directory for PERSONAL\SRIRAM.TXT, which in turn involves looking in the PERSONAL subdirectory for the file SRIRAM.TXT).
Every disk has a root directory Which is the main directory that everything else is part of. The root directory is called “\”, so you can use absolute Pathnames Which is the main directory which don't depend on what your Current directory is. A name like SUVAM\LATTER1.TXT always refer to the same file regardless of which directory you happen to be working in at the time; “/” at beginning means “start looking in the root directory”, so \ SUVAM\LETTER1.TXT means “look in the root directory of the disk for a subdirectory called LETTERS, then look in the subdirectory for a file called LETTER1.TXT”. Leaving out the “\” at the beginning makes this a Relative Pathname Whose meaning is relative to the current directory at the time.
If you want to refer to a file on another disk, you can put a letter identifying the disk at the beginning of the name separated from the rest of the name by a colon(“•”). For example, A:\ LETTER 1.TXT refers to a file called LETTERS1.TXT in the root directory of drive A. DOS keeps track of the current directory on each disk separately, so a relative Pathname like A: LETTER1.TXT refers to a file called LETTER1.TXT in the currently-selected directory on a drive A.
For convenience, all directories (except root directories) contains two special names: “.” reffers to the directory itself, and “.”refers to the parent directory (i.e. the directory that contains this one). For example, if the current directory is \ SUVAM\PERSONAL, the name “..” refers to the directory \ SUVAM,“..\BUSINESS” refers to \SUVAM \ BUSINESS, and “..\..” refers to the directory “\”.
