Is it possible to have install Windows (bootcamp) ONTO an external drive?

Discussion in 'Windows, Linux & Others on the Mac' started by striders, May 22, 2015.

  1. striders macrumors 6502

    Mar 11, 2009
    I don't have much disk space left (I only have 26GB SSD) on my MBP Retina, but I do have an external 256GB SSD with USB 3.0 enclosure.

    So I was thinking on installing Windows via bootcamp onto the external drive instead of the MBP internal drive.

    Is this possible?
  2. crazyxzer0 macrumors 6502

    Oct 28, 2008
    You won't be able to do it via Bootcamp.

    You can install windows 8 to go onto an external from a windows machine and make it bootable. You will need bootcamp drivers installed but it will work fine.
  3. twocircles macrumors newbie

    Sep 26, 2011
    I’d like to hear details about how this goes and pitfalls to avoid.
  4. striders thread starter macrumors 6502

    Mar 11, 2009

    So I'll need a Windows machine to install another copy of Windows to an external drive. Hmm... I have to find a Windows machine to do this.

    But assuming I have, then it's just a matter of booting up from the external drive by hiding the Option key?
  5. bubulol macrumors 6502

    Mar 7, 2013
  6. yjchua95 macrumors 604

    Apr 23, 2011
    GVA, KUL, MEL (current), ZQN
    You got that right.

    Here's the instructions:
    Windows to Go UEFI

    Connect external drive to Windows VM. You must have a Windows VM in VMware/Parallels/VBox, or a Windows PC. Any existing Windows environment will do.

    Note: If you’re using a 32-bit ISO, your Windows environment used to do these commands have to be 32-bit. And if it’s a 64-bit ISO, the environment has to be 64-bit.

    What you need:
    install.wim file (obtain this from your Windows ISO)

    Open elevated cmd.exe (run as admin)

    Note: All commands aren't case sensitive, including pathway to files.

    Type diskpart
    Type list disk
    Take note of the disk you want to select
    Type select disk 1 (if your disk is Disk 1)
    Type clean
    Type convert gpt (do this and then stop at this point if you're using a drive with a Thunderbolt port. If installing in BIOS-CSM, type convert mbr and then stop at this point if you’re using a drive with a Thunderbolt port)
    Type create partition EFI size=100 (skip if installing in BIOS-CSM)
    Type format quick fs=fat32 label=EFI (skip if installing in BIOS-CSM)
    Type assign letter=S (skip if installing in BIOS-CSM)
    Type create partition primary
    Type format fs=ntfs quick label=W2G (or any other name you wish for label)
    Type assign letter=E
    Type exit

    Open up File Explorer. In your C drive, create a new folder named WIN2GO.
    Put the install.wim file in this folder

    Back in cmd.exe:
    Type dism /apply-image /imagefile:C:\WIN2GO\install.wim /index:1 /applydir:E:\ (this process will take quite a while)
    Type E:\Windows\System32\bcdboot E:\Windows /s S: /f UEFI (use this one for UEFI installation)
    Type E:\Windows\System32\bcdboot E:\Windows /s E: /f ALL (use this one for BIOS-CSM installation)

    Restart your entire Mac. After the chime, hold down Option and when prompted to select your boot drive, select EFI Boot (or whatever else that comes up for a BIOS-CSM installation).

    Proceed installation normally.

    After installation, install Boot Camp drivers. Feel free to trash the VM once you're done too.

    For best results, use USB 3/Thunderbolt. If you don't have USB 3, use Thunderbolt. If you have neither, stick back to the internal drive :)

    Don’t use a USB stick.

    Note: This method involves reformatting the entire external drive.

    For Thunderbolt drives, just boot from the Windows USB installer and install directly onto the TB drive. Windows sees TB drives as an internal PCIe connection. However, you must format the TB drive as GPT first.

    CAUTION: Windows can only be installed in UEFI flawlessly on Haswell Macs and later. Ivy Bridge and earlier Macs can only run Windows in BIOS-CSM flawlessly. Attempts to boot a UEFI installation of Windows on an Ivy Bridge or earlier Mac will result in driver issues.

    These steps do not work with Windows 7, as it lacks the dism.exe utility.

    UEFI-compatible Macs:
    MacBook Air (mid-2013 and later)
    iMac (late-2013 and later)
    Retina MacBook Pro (late-2013 and later)
    Mac Pro (trashcan shape)
    Mac Mini (late-2014 and later)

    Long story short, only Macs with PCIe SSDs support UEFI. Non-retina MBPs, along with other Macs not listed above (basically all Ivy Bridge and older Macs), are not UEFI compatible.

    WinToUSB basically does the same thing, but doesn’t always work because WinToUSB doesn’t really take into account between BIOS-CSM and UEFI Macs; it only uses one method for all (which may result in boot failures and other problems).

    I run Windows off a single Transcend 960GB JetDrive and constantly use it between Macs without problems.
  7. striders thread starter macrumors 6502

    Mar 11, 2009
    Thank you, yjchua95! Really appreciate it.

    I'll try this and will report back if there's any issue.
  8. yjchua95 macrumors 604

    Apr 23, 2011
    GVA, KUL, MEL (current), ZQN
    Note: If your Mac has a PCIe SSD, use the UEFI instructions. Otherwise, use the BIOS-CSM instructions.
  9. striders thread starter macrumors 6502

    Mar 11, 2009

    Got it. I have a MB Pro Retina 2014, so it'll have a PCIe SSD.
  10. yjchua95 macrumors 604

    Apr 23, 2011
    GVA, KUL, MEL (current), ZQN
    That's sweet as, so use the UEFI installation method.
  11. storm78 macrumors newbie

    Aug 21, 2015
    if it would help someone - here is solution:
    using winclone on my imac 27 late 2013 with fusion drive. make a copy, then make sure winclone in options change "Make Legacy Bootable", then remove bootcamp on internal drive (previously installed win 10 btw), then restart entire mac and hold option on loading and choose external ssd thunderbolt for loading.

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