how to create bootable cd

There are many applications for
bootable CDs - the most common
being when undertaking
large roll-outs and when using test
rigs,where it is often useful to combine
operating systems with boot and diagnostic
diskettes to automate the process
of setting up machines.
If you need to repeatedly test from
clean installations it can save lots of
time if you image a disk drive and put
the image, along with the imagingsoftware,
on a bootable CD. It can also be
a timesaver to have frequently-used
boot and diagnostic diskettes on CD,
and it’s an easy way to work with PCs
that do not have a floppy disk drive.
To see if a PC supports booting
from a CD, check your BIOS setup
screens. SCSI drives have their own
BIOS on the adapter; IDE drives use
code in the system BIOS.Most modern
SCSI adapters have a BIOS that allows
it, and most motherboards of the last
two years support booting from IDE
CDdrives. If you are able to change the
boot options, and it lists “CD-ROM”,
your system supports booting from a
CD. If you have a 1995 or 1996motherboard
or SCSI cardthat doesnot support
it, it’s probably worth contacting
the manufacturer - many have BIOS
upgrades available.
Technical Details
When a bootable CD is created, a
“boot record” is put at the very beginning
of the CD, just as it is with a
bootable floppy or hard disk. This record
specifies whether the CD is to
emulate a floppy or hard disk drive,
and contains a pointer to the location
of the actual boot image file.
The El Torito specification, created
by IBM and Phoenix Technologies,
was designed to be completely compatiblewith
the ISO 9660CDstandard.
It adds to the ISO 9660 specification by
requiring a boot record at sector 11 of
the last session on the CD. The boot
record contains an absolute sector
number that points to the “boot catalog”.
There’s no restriction on the location
of the boot catalog.
The catalog contains a list of entries
describing all the “boot images” present
on the CD. Again, there’s no restriction
on where the boot images can
be on theCD. There can be any number
of them, of three different types:
l “Bootable emulation” causes the
image to be mapped to drive A or
C, as a conventional bootable storage
device.
l “Non-bootable emulation” maps
the image as a conventional storage
device, and allocates the last drive
letter to it.
l “No emulation” is a special mode
which loads the image intomemory
and executes it - extremely useful
when developing copy protection
or “smart” CDs designed for a variety
of disparate systems. For example,
the “no emulation” mode is
used in the Windows NT operating
system CDs.
There ismuchscope for systemvendors
to create multi-image CDs where
the boot image is selected dynamically
by the system BIOS, but this requires a
lot of manual assembling and editing,
and is beyond the range of this article.
Although it is relatively easy to manually
assemble the boot catalog, most
BIOSes do not allow selection of the
image and you will have to write a
small amount of low-level systemcode
to do it.
CDs can be set to boot as drive A or
C. The fact that they are a late addition
to the PCmakes them subject to certain
other restrictions. To boot as drive A,
the boot image must be made in the
same format as a 1.2MB, 1.4MB or 2.88
MB floppy disk. The first floppy disk
drive, if present, will become the B
drive. If the system has a second
floppy disk drive, it will not be accessible.
If theCDis set to boot as theCdrive,
it replaces the normal hard disk drive
C, and has no size limit other than that
of the CD itself. However, the source
drive image must have only one partition.
This partition must be both the
first entry in the partition table and a
standard DOS partition.
Creating The Image
Most currentCDRpublishing packages
are capable of reading a floppy
disk and creating a boot image from it.
With the appropriate menu choices
made, they will automatically “inject”
it into the CDimage.With thismethod
it is extremely easy tomake a bootable
CD. Some of the more advanced packages
like Nero can create a bootable
CD from any disk image, and allow
fine-tuning of parameters such as the
emulation type and startup message.
The basic process for making a bootable
CD from a floppy disk is as follows:
1 Create a bootable floppy disk that
has all required driver and startup
Update 139 (June 2000) Page 3 File: T1214.1
Bootable CDs are an invaluable aid when dealing with large roll-outs and test rigs, and
improvements in CD writing software have made the process of creating them far simpler.
By Matt Jones
How To Create
Bootable CDs
PC Support Advisor
www.itp-journals.com
Tutorial:Operating Systems
software on it. You will need a CD
driver in order to use the CD in a
conventional manner once the system
has finished booting. It is wise
to use a generic CD driver if you
plan on using it in a few different
systems.
2 Make sure that any path names in
the config.sys andautoexec.bat files
do not specify drive letters.
3 Make sure your boot process does
not attempt to write to the disk. Set
the read-only flag on all files and
write-protect the disk if possible. If
your system tries towrite to the CD
on boot-up, it will crash.
4 Test this disk thoroughly in whatever
PC environments you wish to
use it.
5 Once you are happy with the bootable
disk, create the CD with your
CDR publishing package. Selecting
the “bootable” option will usually
prompt for the floppy disk. Put any
other data onto the CD in the same
session.
Larger Images
If you wish to create a larger, harddisk
type image, there are a few more
things to do. You will need to choose
and size your source image hard disk
carefully. A program such as Power-
Quest’s Partition Magic is very handy
for tasks like this.
Create and test your image in the
same manner as the floppy image procedure
detailed above. When you are
happywith it, use a program likeNorton’s
DiskEdit or PowerQuest’sDrive-
Image to read the drive and create an
image of it in a single file.At this point,
if your CDR publishing software supports
disk file images, you can simply
select the appropriate file and it will
automatically create the correct boot
records.
If your software does not support
hard disk images, it is still possible to
create them if you are willing to delve
into image files and boot records with
a hex editor. This is not as difficult as
it sounds, and Phoenix Technologies
have an excellent guide on how to do
it on theirWeb site at www.ptltd.com.
It should be noted, however, that in
most cases the floppy disk image
method is sufficient because drivers
can be loaded that allowthe rest of the
CD to be mounted in the DOS session.
Tips
l A rewriteable CDR drive is an extremely
useful tool when experimenting
with bootable CDs.
Although your test CDRW may be
unusable in some standard CD
drives, it can be used on themastering
systemif the CDRWdrive is set
as the primary CD, and this is
enough for general test purposes. If
you are planning on making a variety
of bootable CDs, or just experimenting,
CDRW has the obvious
advantage of media cost. If you
don’t have a CDRW, any failed experiments
can be used as multi-session
backups.
l When making hard disk image
CDs, an old hard disk drive around
650MB in sizemakes a useful addition
to your mastering system. As
hard disk images have certain partitioning
requirements, detailed
above, it’s much easier to have a
whole disk to use for your layout if
you are doing this type of work.
l UnderWindows NT, you will need
to have administrative rights if you
are creating hard disk images (this
requires access to all disk sectors).
l It is possible that you will encounter
older CDs that start to boot, fail
immediately and hang your system.
This is because there was no
initial standard for the first few sectors
of CDs and, although unlikely,
somemay contain a correct “validation
entry” without any of the other
required boot files.
CDR Software
Until fairly recently, bootable CDs
had to be made manually with a combination
of low-level tools. Utility programs
such as BOOTISO and
DISKIMG were used to read bootable
disks and write images to disk files.
These disk images were then hex edited
and manually added to the CD
layout.
It has now become much easier,
with many current CDR writer software
packages able to make bootable
CDs from a floppy disk image, a hard
disk or an image file.Notable software
packages are Easy CD Creator, Win-
OnCD, CDRWIN, HyCD and Nero.
The latter is an extremely powerful
tool that offers complete control of the
CD writing process, and can create
bootable CDs for many platforms. It
can also create “oversized” CDswhich
can be used to gain a small amount of
copy protection.
Many of these programs can be
evaluated before purchase, and this is
advisable due to the wide variation in
CDR drivers and hardware.
Copyright ITP, 2000
File: T1214.2 Update 139 (June 2000) Page 4
PCSA
The Author
Matt Jones is a softwaredeveloper
and can be contacted as
matt.jones@itp-journals.com.
Further Reading
El Torito Bootable CDROM Format
Specification.
BIOS INT 13 Specification, including
extensions.
Enhanced Disk Drive Specification.
ATAPI Specification.
ISO 9660 Specification.
PC Support Advisor
www.itp-journals.com
Tutorial:Operating Systems