MS-DOS [Working With Files]

Files organize information that your computer uses. MS-DOS itselfIF is stored in files that are read into memory when you start your system. There are a number of types of files; each file has a unique name and location in addition to a group of attributes that describes it.

Filenames
Every file has a name. Most files also have an extension. The name always appears first, and the extension is always separated from the name by a period, as in the following example:
    myFile.ext
In this guide, the file's name and extension are referred to as the filename.
Names
Each file has a name for identification. For example, the COMMAND.COM file contains MS-DOS commands, and the MOUSE.COM file contains information your system needs if you use a mouse.
The names you choose for files must:
  • Have no more than eight characters.
  • Contain only the letters A through Z, the numbers 0 through 9, and the following special characters: underscore (_), caret (^), dollar sign ($), tilde (~), exclamation point (!), number sign (#), percent sign (%), ampersand (&), hyphencent ('). No other special characters are acceptable.
  • Not contain spaces, commas, backslashes, or periods (except the period that separates the name from the extension).
  • Not be the following reserved filenames: CLOCK$, CON, AUX, COMn (where n = 1-4), LPTn (where n = 1-3), NUL, and PRN.
Extensions
Extensions help you identify the type of file. MS-DOS uses the following extensions:
  • .EXE (executable) or .COM (command) for files that contain programs
  • .SYS (system) for files that contain information about your hardware (for example, your mouse or expanded memory)
  • .BAT (batch) for files containing lists of commands that MS-DOS carries out as a set
When you create a file, you can choose an extension that helps you identify the file. The extension must contain no more than three characters. The filename restrictions regarding characters and spacing also apply to extensions.
Most programs that create files add an extension. It is generally best to use the extension specified.
Types of Files
Much of the information stored in files is text, such as letters, punctuation, and special characters. Because you perform different tasks with different types of files, it is important to be able to recognize the types of files and that each is used for.
 Program Files
Program files contain the programs that your computer runs. Program files usually have an .EXE or .COM extension. Lotus 1-2-3, for example, is stored in a file called 123.EXE.
Spesialized Data Files
It is common for a program to produce files that contain codes which can be used only by that program.
For example, when you create a spreadsheet data file, the spreadsheet program saves the file in a format that only it can read. Sometimes a program assigns an extension to the files it creates. For example, Microsoft Word assigns a .DOC extension to its document files.
 Unformatted Text Files
Unformatted text files contain only text. Almost all computer programs, including MS-DOS, use a system called the American Standard Code for Information Interchange (ASCII) to represent text. Files of this type often have a .TXT extension.
System Files
System files contain information about your hardware and are sometimes called device drivers. These files usually have a .SYS extension.

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