DOS Chapter 1 The boot process

DOS stands for Disk Operating System and in this book we are dealing with a Microsoft variety, namely MS-DOS version 6.22. There are other DOS's; for example, IBM's PC-DOS and Digital Research's DR-DOS. If you have another DOS you will have to find out yourself what works, what doesn't, and what does not apply. An alternative would be to get the MS-DOS 6.22 so called "upgrade" package which has been available on the net. Keep in mind that whenever DOS is referred to in this book it is MS-DOS 6.22 (which I did not choose, by the way, it just happened to be the one which was available to me).
The three major MS-DOS system files are io.sys, msdos.sys and command.com. (In PC-DOS these files are known as ibmbio.com, ibmdos.com and command.com.) When you start your computer, the BIOS (Basic Input Output System) is activitated, which in turn, activates the DOS system files. Without getting into a lot of nitty gritty details, I will suffice it to say that this is the order in which the files are read:
1. io.sys
2. msdos.sys
3. drvspace.bin (optional - needed only to access drives compressed with drvspace.exe)
4. config.sys (optional)
5. command.com
6. autoexec.bat (optional)
All of these files (except command.com in special cases) must be in the boot root, which in this book is always referred to as c:\ (if your boot drive differs, please make a note of this). The special cases of command.com will addressed in the environment chapter.
After preliminary initialization your PC will display "Starting MS-DOS" on the screen. It is at this time, the F5 or F8 key combinations can be used. If F5 is pressed, config.sys and autoexec.bat are skipped. If Ctrl+F5 is pressed, drvspace.bin will also be skipped.
If the F8 key is pressed, the user can step through both config.sys and autoexec.bat one command at a time. If Ctrl+F8 is pressed, drvspace.bin will be skipped. After using F8 or Ctrl+F8, if you decide to carry out all the remaining commands, press Esc; if you decide to skip all the remaining commands, press F5.
The key combination Ctrl+Alt+Del will reboot the computer.
These features are especially useful in troubleshooting config.sys and autoexec.bat.