============ What are MS-DOS internal commands ===========

1. Why are they called "internal"?

   You can use internal commands at anytime at the command 
   prompt. They don't need any other files to support. They are 
   contained  in  the  command  interpreter.  So they
   are called internal commands.  Besides,  because these 
   commands  are  interpreted by the  command interpreter 
   COMMAND.COM, they usually starts faster than external commands. 
   But they usually take up certain amounts of memory for the 
   place of the execution procedures.
   
   Considering the advantages and disadvantages above, internal 
   commands should be common commands that are not very complex 
   to execute.

2. What do they do?
   
   As I wrote above, they are common commands. They are usually 
   for directory and file operations. They are also for batch 
   programs.  Still, some of them are for other settings of 
   MS-DOS and the computer.

3. How can I use them?
   
   To use them, you only need to be at the command prompt. By 
   default, MS-DOS starts up to its command prompt. Also, you 
   can use command prompt in Windows. Please type "command.com" 
   in the "Run" box of Windows 9x or type "cmd.exe" if you are using 
   Windows NT/2000, and you will get to the command prompt.

4. How can I specify a file in the format 
   <drive:><path><filename>?

   A file is located on a certain drive name (from A~Z). The 
   drive names are allocated when the operating system starts, 
   So they may be different from time to time. To make sure 
   which drive contains your file, you'd better specify a drive 
   label to each drive. To assign a label, you can use "label" 
   command. Also you can use Windows Explorer to do this. Then, 
   you can get label information at the command prompt using 
   command "vol".

   There are several different situations when you specify a 
   location. For example, sometimes the command needs a single 
   location, sometimes the command needs a file specifier or a 
   directory specifier. See the following:

   <drive:>
   This can only be a location. For COPY command, you can use 
   this form for the second parameter (the destination). But you 
   cannot use it for the first parameter (the source), because 
   the first parameter can be a file specifier or a directory 
   specifier. If you use specify the drive letter, it means 
   current directory of that drive.

   <path>; <drive:><path>
   This can be either a location or a directory specifier. To 
   XCOPY, DELTREE, MOVE and REN (REN command in Windows 9x, NT) 
   commands, this format means a directory. To COPY command, 
   this format means all files in the directory (as source) or 
   the location of destination files (as destination).

   <filename>; <path><filename>; <drive:><path><filename>
   This can only be a file specifier.

   Listing finished.

   MS-DOS memorizes "current directory" for each drive. 
   It also stores "current drive". For example, if there are A:, C:, and 
   D: available to MS-DOS, you can have each drive a "current directory" 
   by using "CHDIR" command. Also you can use "CD <drive:>" to get 
   current directory of a specified drive. Also, there is a current 
   drive letter. There, a location specifier can contain only a drive 
   name and it will be considered as current path of the specified drive.

   Please notice the use of "." and ".." as the <path> section. 
   Use "." instead of current directory of current drive or 
   instead of current directory of the drive you specify. Use 
   ".." instead of parent directory of current directory of 
   current drive or instead of current directory of the disk you 
   specify. Notice that in MS-DOS, each drive has a "current 
   directory".

5. What do the characters ">", "<" and "|" mean?

   The characters ">" and "<" are redirection operators. 
   They are used to redirect standard input and output. If 
   you have used any C compiler for MS-DOS, you should have the
   knowledge of these things. ">" is used to redirect standard 
   output to a specified file whose name should be written after 
   character ">". Character "<" is used to redirect standard 
   input. Use it after the name of the executable command 
   and put the name of the file for input after it. The 
   command's standard input will be from the file specified.

   Character "|" is a pipeline operator, which means send the 
   standard output of the command on the left of character "|" to 
   the command on the right of it as standard input.