RM Logo
Technical Rating: 
Support Home PageSupport
Print This PagePrint This Page
Add to 'My Library' Add to 'My Library'

How to boot a system from different devices (e.g. a USB device)
Published Date : 31 Oct 2003   Last Updated : 09 Oct 2013   Content Ref: TEC160822  



Modern systems can boot (load an operating system) from a variety of devices. Most systems will contain a hard disk which will have an operating system pre-loaded onto it. As shipped, the system will usually boot to Windows from the hard disk, however a 'boot order' will usually be set in the system BIOS. A typical boot order would be:

1. Floppy drive A:
2. Hard disk C:
4. Other

This means that if a user inserts a bootable floppy disk into the floppy disk drive of the system and switches it on, it will boot to the operating system contained on the floppy disk (usually MS-DOS), instead of booting to Windows from the hard drive.

BIOS boot order

A system BIOS usually contains a Setup Menu which allows the user to set a Boot Order. Usually three or four devices can be specified to be checked, i.e. device 1 is checked and if present, correctly formatted and marked as bootable, the BIOS will attempt to boot (load an operating system) from that device. If this fails, the BIOS will then check device 2 in the boot order list, and then device 3, etc.

Many BIOSes also have a bootable device called 'Other'. This means that if booting from the first three or four specified devices fails, the BIOS will try any other device it can find.

How to set a boot order in the BIOS
1. Switch on (or restart) the system
2. Press the F2 or DEL key when prompted (the screen will usually inform you of the correct key) to enter SETUP
3. Enter the BIOS password (if requested). The normal factory-set password is RM for RM systems
4. Find the Boot Order menu. This is typically found in the Advanced BIOS Features menu or Boot menu
5. Change the boot order to your preference
6. Exit and Save settings

Bootable devices

BIOSes may support some or all of the following list:

   Bootable Devices

BIOS Description Type of Device  Notes
A: Floppy drive boots as A:
LS120 Superdrive/LS120 boots as A:
C: First hard disk (aka HDD-0) boots as C:
SCSI SCSI hard disk SCSI drives may not be supported by your system
CDROM IDE CD-ROM drive boots as A: if formatted for floppy emulation
HDD-1 Second IDE hard disk boots as C:
HDD-2 Third IDE hard disk boots as C:
HDD-3 Fourth IDE hard disk boots as C:
ZIP100 ZIP100 compatible drive  
USB-FDD USB floppy drive Floppy drive with a USB interface - boots as A:
USB-ZIP USB ZIP drive or USB Flash memory stick formatted as USB-ZIP boots as A:
USB-HDD USB hard disk boots as C:
USB-CDROM USB CD-ROM drive boots as A: if formatted for floppy emulation
LAN Boot from a remote server via Ethernet Local Area Network (PXE)  

Note: To boot from a USB device, you must enable Legacy USB support in the BIOS. This is often called 'USB Legacy support' or 'USB Keyboard support'.


A. Only allow booting from the hard disk

set the boot order as follows:

  • First Boot Device: C:
  • Second Boot Device: none
  • Third Boot Device: none
  • Boot Other Device: none

This will ensure that the system will never boot from any other device, even if the hard disk does not contain an operating system

B. Allow booting from a floppy drive and CD-ROM

set the boot order as follows:

  • First Boot Device: Floppy
  • Second Boot Device: CDROM
  • Third Boot Device: C:
  • Boot Other Device: none

This will allow you to boot from a bootable floppy disk or bootable CD-ROM disk (e.g. an RM Recovery CD).

C. Allow booting from a USB flash memory stick

set the boot order as follows:

  • First Boot Device: USB-ZIP
  • Second Boot Device: USB-HDD
  • Third Boot Device: C:
  • Boot Other Device: none
  • Enable Legacy USB (Keyboard) support

This will allow a memory stick formatted as USB-ZIP to boot as drive A:, or if formatted as a USB-HDD device it will boot as device C:. The memory stick must also contain an operating system (e.g. IO.SYS, MSDOS.SYS, COMMAND.COM).

D. Boot from the second hard disk

set the boot order as follows:

  • First Boot Device: HDD-1
  • Second Boot Device: C:
  • Third Boot Device: none
  • Boot Other Device: none

If you have two hard disks, then this arrangement will boot from the second hard disk first (if you have one fitted and it is bootable). By changing the order of the first and second boot device, you can boot to either hard disk as drive C:.

E. Boot from a variety of sources

set the boot order as follows:

  • First Boot Device: A:
  • Second Boot Device: USB-HDD
  • Third Boot Device: USB-ZIP
  • Boot Other Device: Enabled

This will boot to the hard disk by default, unless a floppy disk or memory stick (USB-HDD or USB-ZIP) is inserted.


What is needed on a device to boot to MS-DOS?

In order for the BIOS to successfully load MS-DOS from a boot device it must be 'bootable' and contain the correct information.

  1. The device must be a 'bootable device'. i.e. the manufacturer must specify that it is bootable. Often this means that it conforms to the 'El Torito' boot specification. For instance, many types of USB CD-ROM drives and USB flash memory sticks (pen drives) do not support booting.
  2. The device must be partitioned and formatted in the correct way. When interrogated by the BIOS, the device must report that it is a certain type of device and that it is bootable. Depending upon the information received, the BIOS may treat the device as either non-bootable, a 'hard-disk' or a 'floppy-disk'. For instance, CD-ROMS can contain a 'floppy image' which is bootable. When the BIOS detects this image, it loads the image and treats it as a 'floppy drive' (usually of 1.44Mb or 2Mb capacity) and MS-DOS gives it the drive letter A:. However, the contents of the rest of the CD is not accessible unless the floppy disk image also contains a suitable CD-ROM driver (e.g. OAKCDROM.SYS) and MSCDEX.exe and these are loaded when it boots.
    Similarly, a USB flash memory device must be formatted as either USB-ZIP or USB-HDD using the manufacturers format utility. If formatted as USB-ZIP then the BIOS will treat it as a 'floppy drive' and MS-DOS will give it a drive letter of A: (the floppy disk will have a drive letter of B:). If however, the USB memory stick is formatted as a USB-HDD device, it will be treated as a 'hard-disk' and MS-DOS will give it a drive letter of C:.
  3. The device/media must be partitioned correctly and the bootable partition must be marked as 'Active'. This mainly applies to hard disk devices which can contain more than one partition. A utility such as FDISK or RMPTN must be used to partition the device and mark the partition you want to boot to as the 'Active' partition. Floppy disk emulation devices do not require this as they contain only one partition. In some cases the utility provided by the device manufacturer will partition and format the device and mark it as Active.
  4. The device must contain the correct files. For instance, to boot to MS-DOS you need to have IO.SYS, MSDOS.SYS and COMMAND.COM. These files are typically transferred using a utility such as SYS.COM. Note that the MSDOS.SYS file contents varies depending on whether the device is a 'floppy disk' or a 'hard disk' device.

  1. Does the manufacturer's specification say it is a bootable device (or support the 'El Torito' Boot Specification?
  2. Have you partitioned the device (if an HDD emulation device)?
  3. Have you formatted the device (if an HDD emulation device)?
  4. Have you marked the device's boot partition as Active (if an HDD emulation device)?
  5. Does the device contain the correct files?
  6. Have you set the correct device type first in the boot order of the BIOS?
  7. If a USB device, have you enabled Legacy USB Keyboard support in the BIOS?
  8. Is the device listed on the startup screen just before it boots (use the 'Pause' key to prevent the screen from clearing and allow you to read the startup text)?
  9. If the device type is not included in the BIOS boot order list, enable the 'Other Boot Device' setting and set the Primary IDE device to 'none' (i.e. disable the hard disk). This may cause the BIOS to boot to that device even if it is not listed by the BIOS as a valid boot device.


Possible Issues

Some format utilities for USB flash memory sticks have two alternative settings:

  1. Format as USB-ZIP
  2. Format as USB-HDD

If you format as a USB-ZIP device then you must set the BIOS boot order for USB-ZIP. The device should boot as drive A: (with the floppy disk as B:).

If you format the device as USB-HDD then you must set the BIOS boot order for USB-HDD. The device should boot as drive C:.

However, some utilities do NOT format the device as a USB-ZIP device, but always as a USB-HDD device (even if the USB-ZIP format has been selected). If the BIOS does not support USB-HDD, then this device will not boot (the V-TEC Mformat USB Flash Disk format utility v1.1.1.3). If your system supports USB-HDD then the device will boot as C: instead of A:. You should obtain a later version of the utility from the manufacturer.

More Information


Some notebooks provide a mechanism to allow the user to boot to a different device. This is typically done by pressing a key (such as the <Esc> key) as the notebook is starting. A prompt is usually displayed indicating which key to press.

When the appropriate key is pressed a boot menu will be presented to allow a choice of boot devices.

Note: Many notebooks cannot be configured to prevent this menu from being presented, even to a non-authorised user.

Did the information in this article help answer your question?
Please add any comments about this article in the box below. If you answered No then it is important you tell us why so that we can change the article if required. We can only respond if you log in to the RM Support website or provide your contact details. Note: If you need help with a technical query, please log a call online or telephone our support team.
Thank you for your feedback, which is sent directly to the RM Knowledge team. We address every message received with the intention of improving our Knowledge Library articles. If you have an unresolved technical issue, please contact RM Support.

If this article has not helped provide a solution then it is also possible to log a call...

Document Keywords: usb, boot order, boot device, hard disk, floppy, stick, pen, memory, cd, cdrom, cd-rom, dvd, drive, flash memory, boot, system, different, device, devices, tec, v tec

Please read - important disclaimer information.
http://www.rm.com/_RMVirtual/Includes/csredirect.asp?cref=&title=Standard Content Disclaimer

Top Of PageTop of page