The command.com file is the command interpreter for Windows 9x. The job of the command interpreter is to execute non-graphical applications for Windows 9x. It is located in several places on your hard drive: C:\command.com and C:\windows\command.com, and possibly either C:\windows\command\ command.com or C:\windows\command\ebd\command.com. These additional files provide a small amount of fault tolerance to this file. Windows 9x usually uses the copy located in the Windows folder rather than the copy located on the root of the C: drive. The copy on the root of the drive is only used during the first stage of the boot process, the real-mode portion. command.com is loaded by io.sys and is responsible for the execution of all commands prior to the loading and initialization of the Windows kernel with the execution of win.com.
If something happens during the boot process that prevents win.com from executing, or if you are using a MS-DOS boot disk and you do not load the Windows 9x GUI (Graphical User Interface) - you are faced with a command prompt provided by command.com. If you are unfamiliar with the command prompt, you may ask yourself, "Now what?" The command prompt, which is composed of a C:\> and a hypnotically blinking underscore, looks back at you unyieldingly. Unfortunately, it won't share its secrets unless you ask nicely! If you have a full version of MS-DOS installed on your computer, then you can get help for all commands by typing help or help with a specific command by typing help and the name of the command, like this:
Rather than using the detailed help command, try typing the name of the command followed by the /? switch. This option will usually give you an abridged version of the help information.
If you have opened a command prompt from within Windows 2000 or Windows XP, you will find help for many MS-DOS commands in the Windows Help file (Start → Help or Start → Help and Support).
Asking for help from the command prompt implies that you know what to ask, or at least that you know the name of the command that you need help with. In the case of the GUI, you are given hints and a fairly intuitive way of moving around and accessing information. However, basic functionality at the command prompt requires only that you know a small handful of commands. These commands, covered in the previous tutorial, include navigation commands such as dir, cd, and md; movement commands such as ren, copy, and xcopy.exe; disk-level commands such as format.com; and text manipulation commands such as type and edit.com.
All of these commands happen at the command prompt. You will often have to revert to the command prompt within Windows 2000 or Windows XP to execute command-line programs. In the case of Windows 9x, you may also have to resort to the command prompt when you are unable to load the GUI due to errors in the system configuration.
In this tutorial:
- System Files and the Boot Process
- Power-On Self-Test (POST) Process
- Standard Boot Process for Windows XP
- ARC pathnames
- The device load process
- Loading the shell
- Understanding the Boot Process for MS-DOS and Windows 9x
- win.com and vmm32
- Managing Memory
- Expanded memory
- Upper memory
- Examining Other Boot Process Files