How to create a Bootable USB Device
Bootable USB devices come in different formats, flash or pen drives, external hard drives, and cd/dvd drives.
Not all USB devices are created equal. By that I mean not all USB flash, pen drives can be made into a bootable device. The best way to create a bootable USB drive is to use a utility that writes the files to the device.
The Boot section or sector of a USB uses the same type of file a bootable cd or dvd does the boot.bin and sometimes the boot.cat. To make these files you need a special program such as the ones listed below.
Because more and more manufactures are opting to not put a floppy drive in their computers it is getting harder to make these files because the program that makes the boot.bin and boot.cat use the boot sector and information from a floppy disk.
If your computer doesn't have or support a floppy drive you have two options:
Another thing that has happened with the computer manufacturing companies is that there is no longer any support on the motherboard or in the BIOS for a floppy drive and the floppy disk format so if you have an external USB floppy if it is not supported you can not use it to boot your computer.
And you can not do this to an external USB hard drive, external hard drives take the same procedure that a normal hard drive does.
(To make a hard drive in an external usb enclosure bootable may require you to remove the drive and install it into a computer, this procedure is some what involved and will invalidate a warranty if it is a new device.)
I have found a some utilities that will create a bootable USB device:
Now that you have the utility you also need a bootable floppy with the Autoexec.bat and config.sys files. Once you have created the device you can copy any other files you may need on to it.
Because you can only have one partition on a pen/flash drive adding more 'tools' to the drive has to be done with care and from the Operating System on the drive active.
By active I mean that it is used to boot the computer.
Adding programs and files to the boot drive from another Operating System will corrupt the file structure of the drive making it useless.
Here is a list of 'tools' I use to troubleshoot and repair computers, these tools will help you with your troubleshooting and repairs: Your IT Tool Box. If you are using ERD Commander or BartPE I would suggest you make another pen/flash drive bootable with DOS instead for some of these tools.
Or you could make a custom Emergency Repair Disk (ERD) for Windows 7 /8? Check this out.
You will find more instructions on creating bootable devices in the Self Computer Repair Unleashed! 2nd Edition..