I was going to do a clean install of El Capitan and I created a Bootable USB drive. After making the drive I done the usual, I restarted while I held down the option key to white I was presented a screen with startup disk option screen and predictably I found my usual HDD that my OS is on, my backup drive, and my bootable USB which is called "Windows".

That's weird since I've never installed Boot Camp on this machine.

When I boot from the "Windows" drive there's just a blank screen and the letter "J" flashing on it and nothing else happens.

Just a "J" in the top left of the screen.

What is this?

  • After some trial and error I tried booting without the USB bootable of El Capitan in and the "Windows" boot option that takes me to the "J" is gone.
    – andy
    Dec 12, 2016 at 9:01
  • Ok So I reformatted the bootable drive in a none_Journaled format, Fat32 just to test then tested again. Now a blank drive, still showed as "windows" in the boot screen, when I booted from it it say something like "Unreognised boot section" or something to that effect. I can take this to mean the "J" stood for "Journaled" and it was what happens when you try to boot "windows" from a Journaled drive? Thoughts? Anyone want to test to confirm just so anyone that comes finds the answer?
    – andy
    Dec 12, 2016 at 9:48

2 Answers 2


Obviously something went wrong in making the bootable USB stick. It should be 8GB. Why not use a little tool that does it for you: Diskmaker_X, see http://diskmakerx.com You have to have the OSX installer on your disk: if you already installed it and it is gone, download it again from the Purchased tab of AppStore.

  • That's the thing, nothing at all went wrong, the El Capitan bootable drive is there, i'm just confused as to why the windows one is too.
    – andy
    Dec 12, 2016 at 9:45

Startup Manager detects any bootable media. Since you've designated the drive as bootable, it presumes there's something bootable installed there. You've likely created a bootable Windows drive, so that's what Startup Manager says, even if there's no actual Windows present.

  • I didn't create a bootable windows drive, I wiped a USB and used this guide to create a bootable El Capitan drive osxdaily.com/2015/09/30/…
    – andy
    Dec 12, 2016 at 9:11
  • Did you format it GUID or MBR? The guide doesn't seem to mention that.
    – Tetsujin
    Dec 12, 2016 at 11:49
  • Mac Os extended (Journaled), just so confused as to why it's giving me a non-existent windows boot drive. Windows users get the "J" too booting from USB techsupportforum.com/forums/f217/…
    – andy
    Dec 12, 2016 at 12:05
  • 1
    Mac OS extended (HFS+) is what goes on top of the format type, MBR or GUID. As pretty much every USB will be supplied as MBR, this is still my prime suspect.
    – Tetsujin
    Dec 13, 2016 at 18:21

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