Why fuss with bootable floppy disks that can degrade over time and develop errors when most PCs will boot from a CD? In this Daily Drill Down, Faithe Wempen explains how to use your CD-R or CD-RW drive to make an emergency boot disc CD.

Can your PC boot from CD?
Get a definitive answer to this question before you invest a lot of time and energy in creating a bootable CD. There’s no point in making one if your system can’t use it (unless, of course, you are preparing to use it on another PC).

Whether or not you can boot from a CD depends on your system BIOS and its capabilities. To check, enter your PC’s BIOS setup program (by pressing whatever key the message calls for at setup, such as [F1] or [Delete]) and then look for a boot setting. (In my AMI BIOS, the boot is a separate page in the BIOS setup.)

Depending on the BIOS brand and version, there might be a single boot setting, such as Boot Order or Boot Sequence, and each of the choices for it list a series of drives in a certain order, such as C:, A:, or CD-ROM. As long as CD-ROM is mentioned in the option you choose, the CD-ROM drive will be bootable. (The PC will not actually try to boot from the CD-ROM drive, however, unless the other drives that precede it in the boot order have failed to boot.)

Figure A
Check the BIOS to make sure you can boot from your CD-ROM drive.

Other BIOS programs have several separate settings, such as First Boot Drive, Second Boot Drive, and so on. You must choose an individual drive for each setting. To make the CD-ROM drive bootable, make sure it is selected for one of these settings.

Figure B
Some BIOSs list bootable devices separately.

If the BIOS doesn’t mention anything about the CD-ROM (or ATAPI device) in the boot settings, your computer probably can’t boot from a CD.
You might be able to get a BIOS update from your PC vendor or motherboard manufacturer that will enable the feature. Try the PC vendor’s Web site first; if you can’t find an update there, try the motherboard manufacturer. If you still strike out, try the Web site of the BIOS manufacturer (such as AMI or Phoenix). The reason for this is because PC vendors sometimes customize BIOSs, so if you can get a BIOS update from the vendor, it’ll work best. Motherboard manufacturers also customize BIOSs. A BIOS that’s received directly from the BIOS manufacturer (if you can get one at all) is likely to be generic.
It’s a good idea to test-boot from your CD-ROM drive using a known bootable CD, such as the Windows 98/Me CD, so that if you encounter any problems later with your homemade CD, you will know if the problem is drive-related or CD-related. To do so, you will need to set the boot order in the BIOS to prefer the CD-ROM drive over your hard disk. Then, boot from a known bootable CD. If it works, restart and reconfigure the BIOS to prefer the hard disk again.

What makes a CD bootable?
For a CD to be bootable, it must contain two files: BOOTCAT.BIN and BOOTIMG.BIN. BOOTCAT.BIN is a catalog file, and BOOTIMG.BIN is an image file. The latter contains the needed startup files that one would normally expect to find on a bootable floppy disk. For Windows NT and 2000, that includes the files Ntldr, NtDetect.com, Boot.ini, Autoexec.nt, Config.nt, and Setup.log. For Windows 98 and Me, boot files include Io.sys, Msdos.sys, Command.com, Config.sys, and Autoexec.bat.

When you browse the contents of a bootable CD in Windows or at a command prompt, you won’t see any of the normal startup files that you would find on a bootable floppy disk. This is because they are all stored within BOOTIMG.BIN. When you boot from the bootable CD, everything in BOOTIMG.BIN and BOOTCAT.BIN appears on the A: drive, while everything else on the CD shows up on the regular CD drive letter.

To get started, you must create a bootable floppy disk containing the files necessary to boot from the CD. To create a bootable floppy disk (aka Startup Disk) in Windows 9x/Me, go to Add/Remove Programs in the Control Panel and click Create Disk from the Startup Disk tab. In Windows NT, run Rdisk.exe to create an Emergency Repair Disk (ERD). In Windows 2000, use the Backup utility to create an ERD.

With your newly created floppy disk in the drive, use a CD-writing program, such as Easy CD Creator, to start a new bootable CD layout and specify the floppy disk as the source of the bootable content. The software will copy all the files from the floppy disk into the BOOTIMG.BIN file, and catalog them in BOOTCAT.BIN. Then, when you boot from the CD, it reads these files and treats the CD exactly as it would a floppy disk. (It even assigns the A: drive letter to the content of BOOTIMG.BIN.)

Boot disks and Windows NT/2000
The main purpose for creating a bootable CD is for emergency work—to boot your PC to a basic version of the OS if there is a problem starting normally. This works fine for Windows 9x/Me users, but NT/2000 users are at a disadvantage. That’s because there is no such thing as a true boot disk in NT/2000; at least not in the same sense as in MS-DOS and Windows 9x/Me. Allow me to explain.

In Windows 9x/Me, you can create a Startup Disk that contains the files needed to start the PC and a command interpreter (Command.com). This is essentially a fully functional copy of an OS that you can use to troubleshoot and repair the PC with the help of some command-line utilities. This is not the case with Windows NT/2000. These OSs can create an ERD, but it is not the same as the classic Startup Disk. An ERD contains the startup files and a setup/recovery utility but not a command interpreter for the OS. So when you boot from an ERD, you enter a utility that attempts to repair your Windows installation either using backed-up configuration files stored on your hard disk or using fresh copies of the Windows files from the Windows CD. For this reason, an ERD is useful only on the PC with which you created it. A Windows 9x/Me Startup Disk, however, can be used on any system.
You can start a Windows NT/2000 PC using a Windows 9x/Me Startup Disk, but if the hard disk is formatted with NTFS, you won’t be able to browse its content. You can, however, create a DOS or Linux boot disk with NTFS drivers to browse NTFS partitions from a command line. For information on some free NTFS drivers, read the Daily Feature “Installing Sysinternals’ NTFS for Windows 98 driver.”
The nice thing about the CD format versus the floppy disk format is that there’s plenty of room for extra utilities—all those handy disk fixer-uppers that won’t fit on a single floppy disk. This additional content is much more useful for Windows 9x/Me, since you boot to a command-line interface from which you can run those utilities. Since you don’t boot into a Windows NT/2000 system with an ERD and muck around at the command-line level, your best bet is to boot from the Windows CD or your ERD floppy disk and attempt the repairs using the Recovery option. To avoid problems with floppy disk degradation over time, you can make a CD copy of your ERD, but you probably won’t find it useful to include lots of other content on that CD. You can boot to a Recovery Console from your Windows 2000 CD, however, which gives a command-line interface much like the Windows 98/Me Startup Disk. For more information on the Recovery Console, read “Using the Recovery Console option in Windows 2000.”
You can always put a complete copy of Windows NT/2000 on your bootable CD for reinstallation purposes, but if you’re going to do that, why not just boot from your original Windows CD instead of creating a homemade disk? If you are interested in making a bootable CD of Windows 2000 from CAB files, here is a very helpful article that explains how.
Setting up your software to create a bootable CD
Your CD-RW drive probably came with CD-mastering (that is, burning) software, and that program will probably let you create a bootable CD. Some software treats a bootable CD as a separate type of CD layout, like data versus audio. With other software, you can select a Bootable option in the CD properties. Check your documentation to find out which is the case for your software. The examples in this Daily Drill Down show Easy CD Creator 4.0, which is what came with my CD-RW drive.

To start a bootable CD In Easy CD Creator 4.0, from the menu, choose File | New CD Layout | Bootable CD. The program asks the location of the bootable floppy disk from which you want to copy the files. (You can also specify an image file if you have created one for this purpose.)

Figure C
You can often create a bootable CD from a floppy disk image file.

The software then places BOOTIMG.BIN and BOOTCAT.BIN in a new empty CD layout. You can add additional files to the layout, or you can burn the CD as is. You can then add other files to the CD layout, just as you would when creating a data CD with your CD-writing software. When you boot from the CD, the contents of BOOTIMG.BIN appears as if it were on the A: drive, and all the rest of the content of the CD appears as if it were on the CD-ROM drive letter. When you create a bootable CD with your CD-writing software, it automatically sets the file system to ISO 9660. It is necessary to do this when working at a command prompt because long filenames are not supported.

Note one small quirk: For the system to use the CD-ROM drive at the command prompt and access those additional files on it, real-mode drivers for the CD-ROM drive must be loaded. If you created your BOOTCAT.BIN and BOOTIMG.BIN based on a Windows 98 or Me Startup Disk, this is taken care of for you. When presented with the startup menu, simply choose to start the PC with CD-ROM support, and the needed drivers load automatically.

If you start from a Windows 95 Startup Disk, you must edit the Autoexec.bat and Config.sys files on the startup floppy disk (or create them if they’re not there) before making the CD. You can use any text editor, from the MS-DOS editor (Edit.exe) to Notepad.exe in Windows.

To Config.sys, add a line that loads the driver for the CD-ROM drive, like this:
Device=mydriver.sys /d:mscd001

Substitute the actual name of the real-mode driver for your CD-ROM drive for mydriver.sys. (The driver probably came on a floppy disk when you bought your PC or your drive.) Then, copy the driver file to the startup floppy disk, so it’ll be available when called for.

To Autoexec.bat, add a line that loads MSCDEX.EXE:
MSCDEX /d:mscd001

Then, copy Mscdex.exe from your hard disk to the floppy disk. (Try looking for it in C:\Windows\Command, or use Find in Windows to locate a copy.)

If you want to assign a specific drive letter to the drive, such as Z, add a Lastdrive=Z statement to Config.sys and add /l:z to the end of the MSCDEX line in Autoexec.bat.

What else to put on the CD?
You have a lot of extra room on your bootable CD, so what should you fill it with? You probably have your own favorite command-line and MS-DOS-based disk utilities for troubleshooting, which you will want to include. If you create your BOOTIMG.BIN from a Windows 9x/Me boot floppy disk, you won’t need to include utilities like FDISK and FORMAT on your CD because they are already on the boot floppy disk. (In Windows 98/Me, they are compressed, and when you boot from the disc, they get decompressed onto a RAM disk created on the fly.)

You may also want to think about the steps you would follow if a major problem were to prevent you from starting Windows. Then, use the tools you need for those tasks as a guide. For example:

  • You might want to check for viruses and remove any that you find, so put an antivirus program on your CD. In this case, you don’t want the full Windows version; you want the DOS-based mini utility that your antivirus program places on an emergency boot disk when it creates one. The best way to get at this utility is to create an emergency boot disk with your antivirus software and then copy the contents of that disk to a new folder on your hard disk. Then, include that folder in your CD layout.
  • You might need to reinstall Windows, so perhaps you will want a set of CAB files for Windows on your CD. These take up a lot of space (200 MB or so), so if you already have a bootable Windows CD, this might not be worthwhile. That’s up to you.
  • You might need to repartition and reformat a drive. These utilities (FDISK and FORMAT) are already included in the boot files from the bootable floppy disk you created BOOTIMG.BIN from, so no additional utilities are necessary. However, if you have a favorite version of these from some other source, feel free to include them.
  • You might need to reinstall drivers for your essential hardware components, so you will want drivers for your video card, network card, modem, sound card, printer, and other components. Even if you already have these on other discs, it can be nice to have them all in one place.

This CD will not be large enough to function as a real backup of the whole system, of course, but it should contain the minimal programs you need to get back up and running. You can then restore your critical data files and applications from other sources.

In the event of a system problem, using a bootable CD offers many advantages over using floppy disks. Not only will the information be more permanent, but the large capacity of a CD allows you to store many more utilities than you would otherwise have available, making it easier and quicker for you to get your damaged system running.
The authors and editors have taken care in preparation of the content contained herein but make no expressed or implied warranty of any kind and assume no responsibility for errors or omissions. No liability is assumed for any damages. Always have a verified backup before making any changes.