The A+ Exams Guide: (Exam 220-301), (Exam 220-302) (TestTakers Guides)

DOS is a 16-bit (FAT16), command line driven, text-based operating system. Microsoft’s version of DOS is called MS-DOS. IBM’s version of DOS is called PC-DOS. Our study and the current CompTIA exam focus on MS-DOS, which we refer to from now on simply as DOS. Microsoft has introduced 12 versions of pure DOS since the original 1.0 version. There is no need for you to study or memorize the fine details of each separate DOS version for this exam. However, it is important for you to understand how a ‘pure DOS’ environment works in order to understand how and why we still use the command prompt in newer releases of Windows. It is also important to note that not all DOS commands and functions are interchangeable between DOS versions and operating systems.

Windows 3.x and Windows 9.x require DOS and DOS system files in order to boot and function properly. These operating systems are basically GUIs that sit on top of DOS. Windows 95 attempted to separate from ‘pure DOS’ with its implementation of DOS version 7.0. Windows Me/2000/NT 4.0, and Windows XP include specialized system files that allow them to boot and function without the necessity of DOS.

Command Interpreter

All Windows operating systems use a command interpreter. The command interpreter, also called a command processor, is a program built into an operating system that has the ability to interpret entries and make decisions based on the data entered with a mouse, keyboard, or other input device.

DOS, Windows 3.x, Windows 9.x, and Windows Me use the DOS file COMMAND.COM as the shell, or command interpreter. COMMAND.COM basically waits for instructions to be entered at a command prompt. It then makes a decision on whether to pass the instructions on to a program or display, such as an error message to the screen.

Unlike the version of DOS used with Windows 3.x and Windows 9.x, a file named CMD.EXE actually carries out the instructions entered at the Windows NT/2000/XP command line. In other words, CMD is the command interpreter for Windows NT/2000/XP.

The DOS file COMMAND.COM is actually a utility program that contains internal DOS commands, such as the DIR and COPY commands.