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Booting-up Bootable CDs

Quick Start:- Check (a) that the drive can read the disk and that it is a bootable disk, (b) that the first choice in the BIOS boot order is CDROM and (c) that you are not missing any prompts to press a particular <HotKey>. If all else fails jump down to [Indirectly Boot-up a CD].

It should be simple to just insert the CD and restart one's computer. However, it doesn't always work. We may not have covered everything but you should maybe note that in order to boot to a CD the following should apply:-

[1] Bootable CDs

Booting to a CD requires that it conforms to the El Torito Specification (73k pdf) and has been correctly prepared to make it bootable. Most, but not all, Windows installation CDs from Win98 onwards should be bootable. The full retail or OEM Windows CDs are usually successful. Upgrade CDs (presumably because they anticipate an existing operating system from which setup would be run from within Windows) are not usually, if ever, bootable. The brilliant IsoBuster (2.4MB/Free) can read a CD in Windows to see if it was created with a boot sector inside it.

[2] Readability

A defective or dirty or scratched CD disk or a defective CD drive can mean that a disk is simply unreadable. Successfully booting to the same disk and/or drive in another working system can be a very helpful troubleshooting method. It can also be useful to know whether one can simply access the disk using a boot floppy diskette that has CDROM support as per most at Blowing out dust and running a special lens-cleaning CD can help improve the situation. Manufactured CDs that have been pressed (not burned) should be less problematic than ones burned onto CDR or CDRW disks. When it comes to such burned media, older CD drives, in particular, may have difficulty in reading the disks at all. Also some makes of media may work when others fail.

[3] BIOS Support

Your BIOS must support and "see" your CD drive in order to use it at all. It must also support it as an IPL Device in order to be able to boot to it.

The motherboard's BIOS (Basic Input/Output System) stores its own basic on-board hardware information on an EPROM chip and begins the boot process. It is basically a software program embedded on a "ROM" chip. Some of the same program's settings can be modified/customised and stored on an associated CMOS memory chip; a chip powered by a "watch-type" battery.

The BIOS settings are accessed through a "BIOS Setup" facility (see below). All the connected hardware devices (eg the Hard Drives) are polled by the BIOS start-up routine and certain information from these devices' own ROM chips (also known as firmware) is also stored in the CMOS memory. Sometimes such information is updated automatically; sometimes not. It may be necessary in some circumstances to allow this information to be updated anew by "clearing the CMOS". This can be done by powering off the computer and removing the little battery for an appropriate time or by shorting a special "jumper" on the motherboard, while there is no mains power to the computer.

A flat battery will need replacing since it will not retain the settings stored in the CMOS memory.

[4] Boot Order

Once you get into the Setup facility look around for the Boot Order. As long as the boot order has a CDROM setting then put it first before the HDD (best while troubleshooting) or else choose Floppy then CDROM then HDD (which will allow booting to a floppy if one is in its drive or to a CD if a floppy is absent). In most Setup programs you must ensure that you save any changes you make; usually with the <F10> key. The various options of how to navigate the Setup program will usually be to the right-hand side or on the bottom of the screen. PCs commonly ship without the CDROM being in the boot order - presumably to increase the speed of boot-up. On some PCs there may be another key you can press to enter a specific boot order menu without entering the Setup. Dell PCs, nowadays, commonly use the <F12> key for this. If there is no CDROM setting anywhere in the BIOS Setup you will not be able to directly boot to a CD using the BIOS.

[5] On-Screen Messages and "Emulation"

Bootable CDs basically contain two separate "parts"; a bootable part and a CD-data part. The bootable part can be arranged to use either (i) floppy or (ii) hard drive emulation or indeed (iii) to use no emulation at all and simply run some machine code.

Bootable DIY CDs typically use floppy emulation. These emulated floppies typically run DOS or Linux and use the image file of an actual floppy which is burned to a specific location on the CD. This area on the CD (which can be viewed or extracted using programs like IsoBuster) is accessed during boot-up and the screen display then mimics what the original floppy would have portrayed. Thus a typical Windows 98 start-up floppy-image would (even though running from a location on the CDROM) still prompt you whether you want CD support or not. In such a case you would still need to choose "With CDROM support" in order to be able to access the "CD part" of the same CDROM!

Bootable Windows Installation CDs typically use no emulation. However you should be on the look out for specific on-screen messages during start-up. In particular look out for a choice between booting to the CD or the HDD or simply for a prompt to 'press any key' to boot to the CD. Miss such a message (which can be very fleeting) and the boot processes will not attempt to boot the CDROM. The options are needed so that, during the repeated reboots of the installation process, the HDD gets rebooted-to by default each time once the initial setup routine has been initiated from the CD itself. If you are using a USB keyboard ensure that your motherboard has 'legacy' support for USB devices and that it is enabled.

[6] Slow Spin-up

There will be times when there is both a good CD disk and drive and the BIOS Setup supports booting to a CDROM and has been correctly configured and yet that disk gets repeatedly by-passed as the set boot device. I believe that one reason for this can be that the CD drive just wont "spin-up" in either the correct or in a timely manner. If you cannot hear the drive spin-up to speed during the boot process then it cannot be read at this time (and even though it may be perfectly readable when accessed from an Operating System). You can try pressing the <Pause> key to halt the progress of the display and see if the drive starts to spin. If so all may be well and you would then press <ESC> to continue booting.

Disabling any quick boot options or specifying that only the CD and no other device is the boot device could be worth trying-out in the BIOS set-up.

[7] Bad or Inappropriate BIOS

One rare possibility for failure has been when motherboards have shipped with a bad BIOS; a BIOS that required an upgrade correction by "Flashing its ROM". Theoretically at least, some older BIOS that didn't support CD-booting could be upgraded in a similar manner. When all else has failed try indirect booting as explained later.

[8] Defective Hardware

Any defective piece of hardware attached to a computer can prevent the computer completing its (PowerOnSelfTest) POST routine and thus prevent access to the BIOS or create a myriad of other unforseen consequences. If in doubt remove as much hardware as possible from the computer and try rebooting.

Not every BIOS reports detection of IDE/ATAPI CDROMs in its setup facility. Most do so in an anlagous way to the detection of IDE/ATA Hard Drives. However if the CDROM has been set as the priority boot device a text message will usually be visible on the display showing a message such as "Booting to CDROM" or similar during start-up.

If there is no sign of the CDROM having been detected in the BIOS (usually indicated by a manufacturer or model number under the IDE/ATA settings) or if the CDROM is the priority device and no "Booting to CDROM" message appears on the display during start up you should consider that the drive could be defective or that its jumpers are wrongly configured or that its cables or connections are loose or damaged. If the CD can be read from a floppy or from Windows then this is obviously not the problem.

Indirectly Boot-up a CD

If you can boot to a floppy diskette and the BIOS supports recognition of the CD drive then it will usually be possible to boot the CD via a good boot manager such as Smart Boot Manager. The program can be used in a number of ways but it is probably simplest to run it from a specially prepared boot floppy diskette as per our Smart Boot Manager (SBM) page. XOSL is also mentioned on the same page and can be another good program for indirectly booting a CD.

BootIt-NG, which is usually one of our favourite programs, can sometimes do this but sometimes fails. For it to have any chance of success the Hard Drive must come first in the boot order and the CDROM come second. One would then choose the "Boot Next BIOS Device" setting from the BiNG menus.

There is a section on this page that implies a possible way of booting to a SCSI CDROM. We believe this is misguided and only allows for access to a SCSI CDROM by providing the relevant driver files and correct autoexec.bat and config.sys files to add to a bootable floppy diskette but not as a way of booting-up such CD drives. They are thus useful files that can help access SCSI CDROMs on an Adaptec controller card but are not really helpful in the true context of this page.

As well as being able to set the boot order in the BIOS setup, some BIOS will also give one an option to choose the boot device with a specific <HotKey> during startup. Dell PCs can commonly do this with the F12 key - so look out for such a message on the first screens after turning on the PC.

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