I currently have a Windows 10 laptop that I am trying to reformat to make it run CentOS 7. The laptop does not have a CD/DVD drive, so I am trying to use a flash drive to reformat it. On Windows, I have used diskpart to clean, create partition primary, and format fs=fat32 on a flash drive. Afterwards, I simply xcopy everything from the DVD ISO file (mounted on my file system) over to the flash drive. At this point, my laptop recognizes the USB as bootable, but when attempting to boot, I get the error message "An operating system wasn't found. Please try disconnecting any drives that don't contain an operating system." Am I missing something stupid?

  • making a bootable usb is not simply copying file. a boot partition is needed in order to tell bios which file to boot upon. finding an usbcreator is quiet easy.
    – Archemar
    Dec 13, 2015 at 9:42
  • @Archemar: Creating a primary partition makes the USB bootable. From there, you just need to tell the USB what to boot by copying the files. A USB creator isn't magic. Also, as I mentioned, the USB is bootable.
    – R_Kapp
    Dec 13, 2015 at 12:36

1 Answer 1


The issue was that somehow, the BIOS had defaulted to trying to boot in Legacy mode. Changing that to UEFI mode caused the boot to work fine.

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