Booting in DOS

The DOS Boot Record

To make a disk bootable, certain parts of the operating system must be present. For DOS, this is the two hidden files, IO.SYS and MSDOS.SYS, and COMMAND.COM. These files can

be loaded on the disk when it is formatted, or they can be loaded with the SYS command.

When Windows 95 creates a system disk, it copies these three files to the disk to make the disk bootable.

All DOS boot records, however, are the same whether or not the disk is bootable. When the PC is looking for a bootable disk during POST, if a disk is in the drive, the program stored in the DOS boot record is executed. This program loads the startup files of the operating system.

The boot record contains the names of the two hidden files. For example, for IBM DOS

3.3, the filenames of the hidden files are IBMBIO.COM and IBMDOS.COM. The program looks for these two files on the disk. If it does not find them, a message appears, such as the following:

Non-system disk or disk error...Replace and strike any key when ready...Disk boot failure.

POST terminates until the user intervenes. Only the program in the DOS boot record can

determine if the disk is bootable.

Bootable Disk For DOS

For DOS, make a bootable disk using the same version of DOS that is on your hard

drive. Use this command:

C:\> FORMAT A:/S

The /S option tells DOS to copy to the disk the files needed to load DOS from this

disk. On the disk will be a small boot record that identifies the layout of the disk and

the names of the two DOS hidden files. This command also puts the two hidden files

and COMMAND.COM on the disk.

It’s important that the boot disk has the same version of DOS that is on your hard

drive. By being consistent with versions, once you’re booted you can use some of

DOS loaded from the disk and some DOS program files on the hard drive without

DOS displaying error messages about using different versions of DOS.

Use the VER command at the DOS prompt to display the current version of DOS.

You can also add some DOS utility commands to the disk so that it can serve as a

rescue disk if needed. In addition to the boot files, copy these files to the disk:

ATTRIB.EXE

CHKDSK.EXE

EDIT.COM

FDISK.EXE

FORMAT.COM

MSCDEX.EXE

SCANDISK.EXE

SYS.COM

DEFRAG.EXE

HIMEM.SYS

UNDELETE.EXE

DOS Wildcards

DOS allows you to use wildcard characters to manage several files or directories at one time:

Asterisk (*) stands for any character and any number of characters.

Question mark (?) stands for one character at a time.

For example:

To refer to all files with any name or extension, you would use *.*

To refer to all files that have a two-character extension, you would use *.??

To refer to all files that have a five-character name and any extension, you would use

?????.*