CertiGuide to A+ (Operating Systems)  9  Chapter 0011:  DOS

Identifying the Files 1 The DIR Command

COMMAND.COM has some commands built into it.

Examples of internal commands include;

• DIR (short for directory)
  
  
• DATE & TIME
  
  
• COPY
  
  
• TYPE

Since these are built into the interpreter, they're known as internal commands.

Interestingly, other support programs exist with DOS, however they do not exist inside the interpreter. Rather, they’re stored as separate files on the disk. This is a compromise, because if all the programs were internal, they would be using up memory. In general, the designers of DOS tried to put the most often used, reasonably small, programs into DOS as internal commands, and left the others as external programs.

Examples of external programs include:

• FDISK
  
  
• XCOPY

Since they're not inside the interpreter, they are known as external commands.

When typing a command, at the prompt there will be typing either after a letter followed by a colon (:) - for example, C:\>. This tells DOS that you wish to work with the C drive. This is known as the drive specification. To change the drive specification, simply enter a valid drive letter followed by a colon, then press the Enter key.

DOS is intended to be compact and unobtrusive. This means that when the command has been successfully entered, it does the job it was asked to do, and prompts for more.

Suppose you ask for something that doesn't exist. Perhaps you mistyped a program name. DOS will inform you that it cannot follow your desire with the message “Bad command or file name”, as shown in Figure 137.

There's a standard format for asking DOS to carry out your bidding. This format is called the command syntax, and it governs the way commands are entered. The basic format is:

COMMAND-NAME + modifiers (if any)

Lets look at the internal command function, DIR.

Identifying the Files 1 The DIR Command