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DOS: Creating a boot disk

By Kristin E. Nelson

• DOS based computer
• Printer
• Word processor
• Bootable DOS disk

If you cannot check off the last item in the list above, you should complete your computing tool kit with a bootable DOS disk. This disk allows you to start your IBM-PC/compatible computer with the DOS operating system from the floppy drive, not the hard drive, and perform basic DOS commands. Use a bootable disk:

• To track down the cause of the problem if your hard drive doesn't boot.
• To check for and remove a virus using this disk and Vi-Spy (the University supported antiviral software for IBM-PC/compatibles). For more information on Vi-Spy, search PennInfo using the keyword "vi- spy."
• To start your machine so you can reverse any changes to the autoexec.bat or config.sys files if you've accidentally deleted or made changes to them.

1. Use Vi-Spy to check for computer viruses. You should create a DOS boot disk when your system is "healthy." It should be functioning properly and free of viruses.

2. Insert a blank floppy disk into the A: drive (3.5 inch or 5.25 inch).

3. At the DOS prompt <C >) type FORMAT A:/S or the appropriate variation below.

   If you use a DS/DD 3.5 inch floppy disk in a high density drive, type FORMAT A:/T:80/N:9/S instead; for DOS 5.0 or greater, FORMAT A:/F:720/S will also work.

   If you use a DS/DD 5.25 inch floppy disk in a high density drive, type FORMAT A:/4/S.

   The /S switch makes the disk bootable and places three files on the floppy. Two of these are hidden (you won't see them); the third, command.com, provides basic DOS commands such as DIR and COPY. Note that versions of DOS prior to 3.3 do not copy the command.com file; users of those versions need to copy the file to the disk.

4. A bootable floppy disk with the command.com file is normally enough to troubleshoot problems with your machine. You may, however, want to copy additional files, such as those listed below, to the bootable disk. These files are normally found in a DOS subdirec- tory on your hard drive or in the root directory (C:\). To copy files to your bootable disk type COPY <filename> A: at the DOS command prompt, substituting the name of the file you want to copy for <filename>. Note: All of the files should fit on a high density boot disk; choose the optional files most appropriate for your needs if all of the files will not fit on your low density floppy disk.
   • edit and qbasic--files needed to use the screen text editor for DOS 5 and greater.
   • edlin--line text editor for any version through DOS 5
   • undelete and unformat--To recover from unintentional file deletion or formatting (DOS 5 and greater).
   • fdisk--To configure the hard drive.
   • chkdsk--To obtain information about a floppy disk or hard drive.
   • format--to format a floppy disk or a hard drive.
     (The files above may have the extension .exe or .com depending on your version of DOS.)
   • autoexec.bat and config.sys--These two files are customized for your machine. You may want to put these into a subdirectory on the bootable disk as a backup. Remember to update your boot disk if you change the autoexec.bat or config.sys files on your hard drive.

5. Write-protect this disk by moving the tab on a 3.5 inch disk to reveal the hole, or covering the disk notch on a 5.25 inch disk with a write-protect tab.

6. Test the bootable disk by restarting your machine with the disk in the A: drive. Your machine should start from the floppy disk in drive A and display the A> command prompt.

7. Label the disk with the version of DOS you used to create it, then store it in a convenient but safe location, just in case you need to use it.