How can I make a bootable usb drive using windows only

Discussion in 'iMac' started by raudbul, Aug 18, 2015.

  1. raudbul macrumors newbie

    Aug 20, 2014
    I somehow lost my MAC partition on my iMac and now I only have Windows 8.1. I want to upgrade to Windows 10 but I want a clean install which I can only get through booting from the usb drive. Whenever I get to the boot menu (after holding the alt key) the usb doesn't appear as an option to boot from. I think this has something to do with the way my usb is formatted because it works fine on other PCs. Remember , I can't use the Boot Camp Assistant which looks to be the solution to this kind of problem. I only have Windows 8.1 on my hands and that's it. Please help me.
  2. Thomi2 macrumors newbie

    Aug 21, 2014
    It has to do with different architectures.
    While Windows PC usually uses BIOS, Macintosh uses UEFI. That's why if your bootable USB isn't formatted the right way, Mac will simply ignore it as it cannot detect it.

    To make your USB drive appear in the Alt/Option Mac boot screen, you should:

    Attention, the following only apply if you have another computer handy.
    If you have a Windows computer handy that's perfect.
    Otherwise it will be more difficult to make that work.

    - Download the good tool Rufus, it's a USB bootable media creator very efficient.
    - Have your Windows 8 iso file handy.

    When all the pre-requesite are done, follow these steps.

    What you should know at this point is that if you want your USB drive to be recognized under your Mac, you'll have to to make it recognizable for UEFI systems.

    In Rufus, load your iso image via the little CD ROM button.
    Then choose your USB drive from the list.
    (Check twice you don't have the iso file in the disk you are going to use, the process will not work otherwise as the USB drive needs to be totally wiped out)
    By the way, make sure to backup all data in the USB drive before starting process. As said before, all data will be wiped out in order to prepare the drive.

    Once the little check routine is done, you'll need to partition your USB stick.
    Several options will show up.
    Choose either "MBR partition for UEFI systems"
    "GPT partition for UEFI systems"

    For the facts, GPT stands for Guid Partition Table, which is the partition table recognized by default by UEFI systems.
    I haven't tried the GPT partitioning option, although I don't see why it shouldn't work.

    MBR for UEFI will work as the UEFI built-in into your Macintosh will recognize the MBR partition and will sort of emulate a BIOS (CSM) so that your install of Windows 8 can start.

    In Rufus still, you might see a third option that looks like "MBR partition for BIOS or UEFI systems"
    Avoid selecting this option. Looks like it might not work.

    Then you have another (last) option to select, it's the format of the USB drive.
    FAT32 sounds like the best option, it doesn't really matter as when installing Windows will be reformatted in NTFS anyways.
    NTFS may not be fully supported by Macintosh
    although you can try if you want.

    And that's all! You can launch the process.
    It will warn you all data on USB will be erased and then start the process. It might take a while.

    That's the relaxation part. The computer works on its own.

    Once it's done, your USB is ready!
    Just plug it into your Mac computer, and redo the process Alt/Option etc.

    If you see the USB drive, perfect! Windows setup will boot up and you can perform your Windows install.
    If the USB is still not there, it means it may be still recognizable for BIOS systems.
  3. raudbul thread starter macrumors newbie

    Aug 20, 2014
    Thanks a lot for taking the time to write this, Thomi. Ironically, I actually used Rufus to install the Win10 iso since the first time but the only difference was that I chose "MBR partition for BIOS or UEFI systems" which may be the cause of the problem. I am going to retry the procedure with "MBR partition for UEFI systems" and hopefully the device will be recognized. I'll get back to you after trying this out. Again, thanks.
  4. raudbul thread starter macrumors newbie

    Aug 20, 2014
    Well, following your advice I was able to finally boot from the flash disk. However, whilst the installation I couldn't install windows on any of the partitions I have on the hard drive. It is because I needed to convert it to GPT since it was in MBR format. Formatting the whole hard drive wasn't an option because one of its partitions had all my data. I wanted to format only one partition but apparently it wasn't possible. The only possible way was to format it all and then divide into new partitions. I guess I'll never feel the beauty of a clean win install on this iMac :p. Thanks for your time.
  5. Thomi2 macrumors newbie

    Aug 21, 2014
    Oh I'm really glad you made it to boot from the USB drive via the Macintosh Boot manager! :)
    Everything's not lost, as I read it seems like you're trying to Format the partitions.
    Instead, you should try do Delete them. Windows setup allows those two different options and they are accessible under "Advanced options" when you're prompted to choose where to install Windows.

    Attention, if deleting a partition, all data on the partition you are deleting will be wiped out.
    -> If you delete multiple partitions, Windows will reunify them in one "partition" called "Unallocated Space"

    Unused space Windows setup will reformat into NTFS and will be chosen as default partition to install Windows.

    If your partitions have descriptions ex: E:BootCamp
    It might be easier to find the one you don't want to delete.

    This option might be better than the Format, because it might create a new partition system, which by default will be NTFS.

    Although there's something I don't get because you don't need to partition into GPT, this format is not the one used by Windows. The setup will automatically choose the best file system for the hard drive which again here is NTFS.

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