Windows 7 External HDD Installation?

Discussion in 'Windows, Linux & Others on the Mac' started by Smithy122, Mar 6, 2015.

  1. Smithy122 macrumors newbie

    Dec 12, 2014

    I have gone through the searches o the forum, however, can't appear to find anything which simply answers what im looking for, one could say a quite easy question.

    Essentially, im looking to Purchase Windows 7 so i can use it on my 27" iMac. My iMac has a 250Gb SSD and connected i have two 3TB External Hardrives for my main use.

    I was hoping, that i could purchase a Separate, 500GB External USB 3.0 Hard Drive, to then install Windows 7 on via Bootcamp, and just plug it it when needed and access it when needed.

    However, after a quick read of this forum it appears that, that is not possible.

    I am now under the impression, that you can not install Windows 7 on an External Drive, and even if you can, it is not a simple task.

    Can anybody confirm this for me?

    Furthermore, if it is true that i can not install Windows 7 on an External, and thus in turn forced to Partion my SSD, will there be any longterm effects on that performance wise, i.e if i one day remove it, or in general any performance issues when not using Windows, but on Mac.

    If i do Partion it, i only plan on it being around 60GB, i require it for some Steam games which aren't available on Steam for Mac, nothing major or extravagant and in all honestly it will rarely be used.
  2. m98custom1212 macrumors 6502

    Jul 20, 2013
    Toledo, Ohio
  3. yjchua95 macrumors 604

    Apr 23, 2011
    GVA, KUL, MEL (current), ZQN
    I've only tested this on Windows 8.1, but not on 7. These steps worked for me for Windows 8.1.

    As you are using Windows 7, use BIOS-CSM methods even if you're using a UEFI-compliant Mac. Windows 7 does not support UEFI well.

    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.

    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 (stop at this point if you're using a Thunderbolt drive)
    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.

    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 :)

    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.

    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)

    Non-retina MBPs 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).

    Footnote: Why not just use Windows 8.1? It's faster and better than 7. I don't get why people hate it.


    See my post above.
  4. Smithy122 thread starter macrumors newbie

    Dec 12, 2014
    Thank you for your detail reply, i appreciate it.

    Prior to your response, i stumbled across an article/how to on this website (

    After reading it thoroughly, and being in possession of all the necessary ingredients, i wondered your thoughts on this, does this sound like it would work?

    I.E, i purchased a Simple Segate/WD External USB 3.0 Hard Drive, a Genuine Windows 7, and had access to a Windows 7 64bit PC/Laptop - I will be able to perform this task, and in essence, 'Plug & Play Windows 7'

    Therefore, when i want to use my Windows 7, i simply plug in the USB for the New External HDD with it on, and then restart, press Alt, and access it?

    It seems the article suggests that and people replying have had success. Based on your reply to my above, i would appreciate your understanding of this article, as im pretty new to this topic.

    *Edit - As per your footnote, i read some issues with Steam/Some games using Windows 8. Considering Windows 7 is Cheaper, and the future upgrade to windows 10 is Free for Windows 7 and 8 which will be out this year, i figure it might be easier.
  5. yjchua95 macrumors 604

    Apr 23, 2011
    GVA, KUL, MEL (current), ZQN
    My method was similarly based on that article you provided as well, but modified in some places here and there to allow for native UEFI booting.

    And yes, in essence, that's how it works. However, my method uses dism.exe instead of having to download the entire WAIK (and imagex.exe). dism.exe is built into some Windows versions (I know that 8.1 Pro has it), so you can save yourself the trouble of getting that.
  6. Smithy122 thread starter macrumors newbie

    Dec 12, 2014
    Thank you again for your response, along with your confirmation and clarification.

    Looks like something i shall invest in then
  7. doynton, Mar 7, 2015
    Last edited: Mar 7, 2015

    doynton macrumors 6502

    Oct 19, 2014
    For your preparation list, I don't know if you missed the bit in yjchua95's post..
    you don't need access to a real windows laptop - you can use a VM if you want.

    If you use the Windows 10 preview iso to make the VM you can use dism as above (Windows 7 doesn't have dism - you have to download WAIK and use imagex). You'd have to use VMWare fusion (demo - no need to buy it) as Virtualbox doesn't support USB3. Parallels might work but I've never used it.

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6 March 6, 2015