What does a bootable USB flash drive do?

[WhyPi77]

I was attempting to run windows off a mac by booting off an external hard drive, but when my MacBook recognized the drive as EFI I knew it wouldn't work. I read about making a bootable USB flash drive with Rufus, but I was unclear what that would do. Would it install Windows on my hard drive?

 

[jsmithepa]

Mac can boot OSX from an external, but I dunno whether a Mac can boot Windows from an external. In general, Windows can't be boot from an external.

A Bootable USB Flash, is exactly that, the flash has been formatted with a bootstrap loader and contains an OS to boot with, NOT Windows. Don't ask us, ask Microsoft.

Rufus, one of its popular function is to boot with a Windows install ISO, so you can INSTALL Windows from a flash, not requiring a CD/DVD.

 

[Promomilia]

1. Download the on top of archive
2. Extract it to your desktop
3. Insert your USB flash drive
4. Launch the HP USB Disk Storage Format Tool
5. Give the Flash Drive a name (example: USB FLASH STICK)
6. Check the checkbox for Quick Format
7. Set the File System to the FAT option (Note, if you do not see FAT, reference this post by katalin_2003)
8. Click on 'Create a DOS startup disk', select the radial for 'using DOS system files situated at:', click the '...' button and point to the directory (part of the downloaded archive) titled "MiniDOS".
9. Click Start