Boot CD's Explained

and How to Make your Own

Here is my own simple Win98 DOS boot CD ISO - open in any CD burning program and burn.  It has the basic DOS files and  NTFS4DOS (Read/Write) for drives LESS than 137 GB, and ReadNTFS for any size NTFS drive (but it only supports Read Only, so all you can do is copy files "from" the NTFS Hard drive to another drive which must be FAT32).

*** This is why I always make my Windows Hard drive partition FAT32 - not NTFS - so I can repair it with a Boot CD

For Internal CD/DVD drives - you will see an A drive and a K drive

For external USB drives - you will see only an A drive

The Bootable CD  -  one of the most mysterious and least talked about item - but an item that you most certainly will need.

Floppy Emulation vs no Floppy Emulation - any boot CD you make on your own will have to use Floppy Emulation.  Non floppy emulation boot CD's are made by Professionals who know the Boot Sequences inside and out.  The floppy emulation CD is limited in viewable size because the system is tricked into thinking that it is dealing with a Floppy !!  The no Floppy Emulation CDs can be full of files that are only limited in size by the CD size.  Yoy can also have non Emulation Boot DVD's (such as Windows Vista) when very large storage is required.

Boot Floppy Diskettes

To understand a Boot CD you must first understand a Boot Floppy (also see Disassembly of a Floppy DOS boot Sector or even better, see MSDOS 5.0 Floppy Boot Record).  We all know and have WinXP boot CD's.  Usually that's enough.  But there are times you may need to boot into DOS, which in the past, you would get out your old, trusty Win98 boot floppy.  It allowed to to see the files on your hard drive so long as your drive was FAT32.  And in the case of NTFS all you had to do was download Active's NTFS DOS Reader and/or Active's NTFS DOS Read/Write software.

The boot sector of a floppy disk is located at cylinder 0, head 0, sector 1. This sector is created by a floppy disk formating program, such as the DOS FORMAT program. The boot sector of a FAT hard disk partition has a similar layout and function. Basically a bootable FAT hard disk partition (the MBR - Master Boot Record - also see Disassembly of an MBR)  looks like a big floppy during the early stages of the system's boot processing.

Entire Boot sector in hex and ASCII of an MSDOS 5.0 Floppy

The File Allocation of a Floppy, unlike Hard Drives which are either FAT16 (old), FAT32, or NTFS  -  is FAT12.  The following is an older 1.2 MB 5.25" floppy but the boot sector is basicallt the same as with a modern 1.44 MB 3.5" floppy"

There are a number of hidden bytes in a boot sector that are NOT in files but are used by the computer in the boot routine.  This is a special case since everything else runs off of files.  There are, however, 2 file names (NOT the Actual Files !!) in the boot sector:  IO.SYS and MSDOS.SYS - they are normally hidden, system files and they reside on the other portion of the floppy.  The names are in the boot record because the files need to be accessed during the boot process.  You can use attrib.exe to make them viewable.  The boot sector is "invisible" data - there are no files in the boot sector !!  The boot sector is comprised of the following:

The Structure of a Bootable CD and the ISO Image

A regular CD has files and folders on it that you can see in Windows Explorer.  The ISO of a regular CD can be opened up and viewed by any ISO uitility, but the most popular is "UltraISO".  The structure of a Boot CD has two sections:

If you use an ISO utility to save the CD as an ISO file, the following is what you will see when you open it in various Utilities:

Ultra ISO and Nero - only shows the main files - the boot sector is invisible

IsoBuster - shows you BOTH the Boot sector files (typically "" and "BootImage.img"), and the main files


Why use a Boot CD ?  PC's with NO FLOPPY DRIVE !!!

They took away the floppy drive on the new machines - now you need a boot CD.  And Boot CD's are EXTREMELY COMPLEX.

There are 4 main cases that you may find yourself in - the only cases where you will typically make your own CD is Case 1 and 3:

  1. Internal CD drive - Boot CD with Floppy Emulation - using a Win98 Boot CD that has the same contents as a Boot Floppy
  2. Internal CD drive - Boot CD without Emulation - typically premade Boot CD's - WinXP CD, UBCD, EBCD
  3. External USB CD drive - Boot CD with Floppy Emulation - using a Win98 Boot CD that has the same contents as a Boot Floppy and a computer BIOS that allows your system to boot from the USB port so long as a device with a boot sector is attached (USB CD Drive with same Win98 Boot CD as in #1, or an external Backup Drive that has been formatted with a boot sector, or a Thumb Drive with Boot sector
  4. External USB CD drive - Boot CD without Floppy Emulation - typically premade Boot CD's - WinXP CD, UBCD, ERCD

Common Types of Boot CD's


*** you should have the following on-hand ***
WinXP bootable CD,  UBCD,  and a custom Win98-DOS boot CD


1)  download an burn one UBCD on keep it on hand for emergencies.  It is complex and loads all sorts of special drivers and create tricky RAM disks in the background.  But it does have a ton of useful DOS apps on it !! 

2)  take your Win98 boot floppy that you have always used, and make your own quick and easy Boot CD from it

The steps are simple once you know how.  But there are two possiblities:

  1. internal CD/DVD drive - you will be able to use MSCDEX to load the CDrom drivers and "see" the entire CD, so go ahead and load it up with whatever DOS apps you want 
  2. external USB CD drive - you can boot from it and see the Boot Sector image using Floppy Emulation.  The pro boot CD use no floppy emulation and all files in the regular portion of the CD are visible


How to Create your own Boot CD

NOTE:  to skip ALL the following Steps completely - download my own Win98 Boot CD ISO file , open it with UltraISO or Nero - and burn

The 5 files required to Boot a CD:

One Boot Catalog, one Boot Sector Image file, and the three system files ( may not be needed to boot but you won't be able to run any DOS commands without it, so it is a critical system file):


Step 1)  use WinImage to convert floppy to a Boot Image file called "BootImage.img"

a)  insert Boot Floppy

NOTE:  if you have no boot floppy or if your machine has no floppy drive you can instead download this standard Win98-SE Image file (*.ima file) as a starting template and skip to Step 2. 
Or if you have not boot floppy but your machine DOES have a floppy drive, then you can create a standard Win98-SE boot floppy from this WinImage Self-Extracting File, and go to the next step.

b) select "Disk/Use Floppy A:" (should already be selected)

c) select "Disk/Read Disk (CTRL-R)" to read in the full floppy contents including the boot sector

d) if you want to leave this as a 1.44 MB emulated floppy CD (standard WinImage file) then leave it as is.  But usually you will want to add more files, so change it to the larger "standard" flopppy emulation size of 2.88 MB.  To do that, select Image/Change Format . . . .  and select 2,88 MB

Onl;y use 1.44 or 2.88 MB  -  do NOT use Custom Image Format
the size will fail to support Floppy Emulation !!

e) add/remove files by selecting files you do not want and hitting "Delete", adding new files by dragging them in from Explorer or by selecting "Image/Inject". 

NOTE: Add items such as the 5 Hives from Windows (corrupt registry problems mean corrupt Hives and you may not be able to boot to Windows - save the existing ones and copy these over them), Fprot (Antivirus), SpinRite (Hard Driver Failure recovery tool), DelPart (delete Partitions), NTF4DOS (Read/Write NTFS with partitions less than 137 GB), ReadNTFS (Read-Only for NTFS but will work with drives greater than and equal to 137 GB), etc. 
DO NOT EXCEED THE 2.88 MB space limitation !!!

NOTE on Config.sys and Autoexec.bat  - since this is a bootable CD with floppy emulation:

f)  File/Save as . . . and save it as an *.ima filetype - for example, BootImage.ima  -  we will use this to create the Boot CD

Step 2 with UltraISO)  use UltrISO to create a bootable ISO and to Burn the Boot CD

a) start up UltraISO, select File/New . . . Bootable CD/DVD Image, and when it asks you where the boot file is, load BootImage.ima

NOTE:  for Bootable CD/DVD's - UltraISO has "Floppy Emulation" turned on by default and there is no way to turn it off.  It does not tell you anywhere, whether the CD ISO you are creating will have Floppy Emulation or not.  If you must turn it off, then use Nero instead.

b) using Windows Explorer, drag any additional files and folders into the right-pane of Ultra ISO

c) File/Save . . .   and save it as an ISO file. 

d)  open your ISO file in "ISOBuster" (free) to make sure that Floppy Emulation is turn ON.  Click the entry called "Bootable CD" on the left and then read what it says on the right next to "BootImage.img":

BootImage.img with "No Emulation"
When the ima file was crated in WinImage - the Image format was selected as "Custom" and set to 10 MB
 this is a non-standard Floppy Image size and therefore failed to support Floppy Emulation. 

BootImage.img with Floppy Emulation
WinImage Image format was 2.88 MB.  whenever it says "size according to specification" then it
accepted the Image Format as standard and was able to use Floppy Emulation

d) close and restart UltraISO and open the ISO file - then burn it to CD

e) edit your setup BIOS screen to boot from CD

f) test your new Bootable Win98 DOS CD by booting with it


Step 2 with Nero)  use Nero to create a bootable ISO and to Burn the Boot CD

a) start Nero Burning ROM

b) select "CD-ROM (Boot)"

c) click "Browse" and load the WinImage ima file

by default, Floppy Emulation should be checked - leave it checked !!

d) click "New"

e) then Burn the CD

NOTE:  it will be created and Nero will rename one of the with the Boot sector files.  The two boot sector files are now:


The Final Results

 If you boot using an Internal CD drive, assuming MSCDEX took the "F" drive:

If you boot using an External USB CD drive, assuming MSCDEX may still appear as if it took the "F" drive, but it will fail to do so:

NOTE:  You may wonder why I include the UltraISO step of dragging in files, even for people that will use the CD for an external USB CD drive - this is to make it a universal Boot CD in case it is ever needed to boot a machine using an Internal; CD drive