Determine whether a usb drive is bootable

To be capable of being made bootable a usb stick has to use an mbr partition table. You may not realise it, but a usb doesn't actually need a partiton table, and many are supplied formatted without one. Such a usb has to be reformatted completely from scratch to give it an mbr in order to make it bootable. This is what the MCT does when it makes a bootable usb, you can also do it yourself with Diskpart.

Edwin has shown examples of the contents of a typical bootable usb from Microsoft. The folders boot and efi, and the files bootmgr and bootmgr.efi are essentials, the rest may vary depending on the purpose of the usb. A bootable Recovery Drive won't have a setup.exe or autorun.inf, for example.

In addition, to be bootable on a legacy bios system the partition has to be marked as Active. You can see if it is in Disk Management.

Thanks for reminding me about the MBR stuff, Bree. It had totally slipped my mind that active + MBR is what it takes to be bootable.
--Ed--

EdTittel said:

Thanks for reminding me ... that active + MBR is what it takes to be bootable.

Remember, that's only required for a legacy bios system, a uefi system doesn't care if the partition is active or not - if the right files are there it will boot.

Yes, but it explains by it's there on a "generally bootable" UFD, suitable for both BIOS and UEFI platforms. So again: thanks, and thanks one more time for the additional explanation.
Best wishes,
--Ed--