I want to install Windows 7 on an external hard drive, and boot from it when needed.

Is this possible on a Mac? I have heard from some sources that it is not possible to boot Windows from external drives, at least on the new Macs. I found this quite surprising.

Any idea if this is true?

  • 3
    possible duplicate of Boot Macbook pro from external harddisk
    – jtbandes
    Commented Apr 18, 2012 at 15:32
  • apparently rEFIt doesnt work ...
    – Newton
    Commented Apr 19, 2012 at 9:40
  • Doesn't work for what? I've used it to triple-boot before...
    – jtbandes
    Commented Apr 19, 2012 at 11:25
  • from an external? what Mac were you using and what OS did it have installed?
    – Newton
    Commented Apr 19, 2012 at 12:38
  • Ah no, just internal, sorry...
    – jtbandes
    Commented Apr 19, 2012 at 12:43

7 Answers 7


It is possible, but it's not straight forward. This detailed step by step guide (which I did) contains all you need to know to install and run Windows 7 or 8 from an external drive (USB3 or thunderbolt): http://bleeptobleep.blogspot.fr/2013/02/mac-install-windows-7-or-8-on-external.html

To sum up, this guide will help you:

  • Get the Windows installation pack from a DVD or ISO file
  • Partition and format your external drive to make it bootable
  • Deploy Windows on your external drive
  • Boot on your external drive
  • Install Windows
  • Download and install the bootcamp drivers (without even using the bootcamp assistant)
  • 2
    Could you please summarize the information here and not just give a link. See these meta questions and here
    – mmmmmm
    Commented Feb 4, 2013 at 13:51
  • Sorry, I added a summary now. Is it sufficient? Commented Feb 4, 2013 at 14:26
  • Hey, please anybody could confirm if it is working ? P.S.: my setup : MBA 2013 + 2 TB WD USB3 External(having 4 partitions 1st NTFS and rest 3 exFAT) Commented May 10, 2014 at 21:02
  • I tried this method and the disk boots fine, however the installation freezes right on the first "Hi there" screen in Windows (where you choose language). I'm trying with Windows 10 and MacBook Pro 15" 2016. It might be because of the lack of keyboard and touchpad drivers, what can I do? Commented Feb 22, 2017 at 11:00

Bootcamp simply isn't designed to install Windows on an external drive.

  1. If I have more than one hard drive, can I install Microsoft Windows on any drive?

    You can use Boot Camp to install Windows on any internal hard drive, but not on an external hard drive.


There is always the possibility to run Windows 7 as a virtual image (e.g. VMWare, VirtualBox). Works well from an external drive and has the advantage that you can start the image from any computer that has the software installed.


Silly as I am I wanted to do the same a few weeks ago. But the Windows 7 installer told me that it can't be installed on an external (USB or Firewire) drive.

You could probably installed a Windows PE version. But since that's not the Real Deal it wasn't an option for me.

Update There's a How-To Install Windows 7 on an external drive which I gonna try in the next few days. Not sure if that's gonna work on a Mac.

Update 2 I tried to install Windows 7 on an external USB drive following the How-To in the first Update. Unfortuantely I didn't get it to work. Getting it copied to the external drive worked well but after rebooting I got an error about not finding this Windows installation.


for straightforward-method, you can install and run a bootcamp Windows on thunderbolt drive

Bootcamp Windows does not support for usb and firewire external drive, but do support for thunderbolt drive

  • 2
    Could you elaborate on how Bootcamp runs on an external drive. The official instructions explain this is not only not supported, but not achievable without modifying the code or the install steps.
    – bmike
    Commented Feb 26, 2014 at 14:44

I have followed BleepToBleep's instruction but couldn't get Windows 7 to boot on external hard drive. It supposed-to-be-bootable hard drive failed to start Windows installation after showing the Windows logo.

So I tried other method and succeeded.

Here is the link: How to install Windows on external hard drive

To sum it up:

  1. Download and install WinToUSB app on a PC or virtual PC.

  2. Partition the external hard drive to have 2 partitions:(similar to BleepToBleep)

    1st partition: 350MB FAT32

    2nd partition: The rest of the hard drive in NTFS

  3. Run WinToUSB with the ISO file of Windows 7 or any Windows

  4. ReBoot the Mac and hold Alt button, boot into Windows and finish the installation. Every times it restarts, hold Alt button and boot into Windows again until the installation finishes.

  5. Download the driver to the Mac.

    If it can be easily found in this link Apple Bootcamp drivers

    If it cannot be found, follow this manual instruction to find. (It will take some time)

  • I tried this method and got stuck when I first booted using the Alt button and then choosing Windows: after a minute of showing intensive activity accessing my SSD attached with a USB3 adapter, the Windows boot logo appeared for about a minute and then I was greeted with BSOD (0x7B).
    – Henno
    Commented May 11, 2016 at 18:44
  • @Henno what is the spec of your Mac? Mine is MacBookPro Retina 15-inch Mid 2014, core i7 2.5 Ghz, 16 GB of 1600 Mhz DDR3. Also what is the Windows version that you tried to install? I notice that Windows 7 may have some issues with USB 3 so I tried Windows 8
    – L N
    Commented May 12, 2016 at 4:48

The key to getting the whole thing to work is to run part of bootcamp - the one which creates a Windows partition - but (and here's the key) to make that partition on your internal hard drive VERY small (<1GB).

Then you can run the Windows install from an external USB. BEFORE running the install, you need to enter CMD within the install utility to "flag" the external hard drive as active and bootable.

I have created a detailed guide here: http://kevtg-compuproductive.tumblr.com

It will work for any Mac, but especially with retina and air users who are having trouble getting other methods to work. The link above is formatted more nicely, but I have pasted the text below. It will work if you follow each step iteratively.

Guide: create external Windows 7 boot drive for Macbook image Perhaps you want or need to install Windows on your Retina Macbook Pro. This is not hard to do, if you don’t mind the Windows partition taking up space on your disk drive -or- if you are willing to deal with the performance degradation from using the virtual machines: Parallels or VMware.
Instead of installing Windows on a separate partition within an internal storage disk, you can opt to buy an external Thunderbolt solid-state drive on which to place the Windows OS. You could just as easily use an external hard drive (instead of a solid-state drive) if you prefer a lower cost/GB. It just won’t be as fast. What these look like: image This frees up your internal drive for all your Macintosh computing needs, while also enabling a large external disk on which to place a robust Windows install. This guide is fairly detailed and only requires that you can follow a series of specific steps. If you can tie your shoes and you can read, you can probably run Windows off an external Thunderbolt drive. A SUMMARY OF THE STEPS (so you know what you’re getting into) It should go without saying, but make sure you have backed up your entire system before you proceed. 1) Resize your internal drive partition to make room for windows boot files WITHOUT using Bootcamp. Bootcamp uses a 20GB minimum and we don’t want to lose that much space. 2) Install Windows on external Thunderbolt drive. 3) Install Bootcamp Drivers THE GUIDE

1) Create a FAT formatted partition within your MBP internal disk. I call this “the sliver” because it is so-so tiny. you can use Disk Utility or Terminal to resize your MBP internal drive A. to use Disk Utility Open it from Applications»Utilities select the Drive from the top of the hierarchy click the “Partition” tab Beneath the “Partition Layout” pane, select your Macintosh HD (or whatever you have labeled you system disk). Mentally now, subtract 1.0GB from the current size of your internal drive. For example, your drive may read 250.14. In the “size” box, type 249.0 You can actually shrink it by as little as 400MB, but let’s leave a little buffer. This is going to allow you to create a new FAT partition into which Windows will automatically place boot files click “Apply” now, click the new blank area below the main partition. Format it to MS-DOS (FAT) Things should look something like this: image B. to use Terminal (faster, but less visual) open terminal: Apps»Utilities Type: diskutil list

You need 2 pieces of information from the resulting table: 1) the size of your main partition and 2) your internal partition identifier (e.g. disk0s2) Double-check. But if you’re typing in terminal you already know that you should be precise anyway now, execute the resize volume command: diskutil resizeVolume disk0s2 249G MS-DOS FAT 1.1G In place of “disk0s2,” insert the identifier for your internal system disk partition. now you have an internal FAT32 “sliver.” Confirm this with diskutil list

Now, there is a SECOND step NOT to be missed: tagging this tiny internal partition as “Active” for the Windows install. Luckily, your Windows install USB/DVD comes with the utility. This is detailed in step 4, below.

2) Create (if you haven’t already) your USB Windows install disk. Go ahead and use Bootcamp utility for this. Just make sure, in the first window, you deselect the last option for “create Bootcamp partition and install Windows.” We already did this. So, select “Create Windows 7 or later … ” and “download the latest Windows support…” Deselect the last option. this will take a while. Sometimes, the utility has trouble getting the support software from Apple (fails). This is fine. By the time it reaches this point, it has already created the boot disk. BUT, this means you have to download the Bootcamp drivers manually. You can download them here. Then copy the Bootcamp_version-whatever folder onto the Windows install USB stick. It has been labeled WININSTALL by Bootcamp. 3) Boot to Windows install. Restart your computer, holding the Opt key at the perfect moment! It can be tricky to time it right. Select to boot from the USB “windows” drive. It is orange. image

4) Mark internal “sliver” as active. After the computer boots to the USB drive, click to select your language. BUT then we need to enter the “Repair utility” to set the small FAT sliver inside the computer to “active.” Don’t worry: you’re not actually performing any repairs. You’re just using the command-line utility that is built-in After you hit “Repair,” go ahead and skip all the automatic options, so that you can use command-line. In order now… diskpart list disk select disk # —in place of “#,” your internal disk listed list partition select partition # —in place of “#,” the sliver FAT partition we created active assign letter=a (or whatever. Get crazy. Call it “Z”) exit 5) Restart computer, hold option at the perfect moment. Select the USB Windows disk again (the orange one). Enter Windows install setup. You know, keep hitting “next, next next,” until…

6) Select a “Custom install,” when presented with the option, so you can select your external Thunderbolt disk to install. Do not install on your internal Mac drive. Do not install on the internal sliver partition. Go ahead and format the whole drive using the Format button, after selecting your external Thunderbolt partition. Don’t format any other partitions The format preserves existing partitions, BUT if you want to create others (perhaps to share with you Mac side) later, you can resize your primary NTFS partition within Windows after you install it.

7) Finish the Windows install. Each time it reboots, you will need to hold down the option key to choose to boot to the new Windows volume you have created during the install. Don’t boot to your USB stick anymore. The Thunderbolt Windows installation appears on the boot option screen as an internal disk, labeled “Windows.” If you miss the timing to initiate the boot menu, don’t worry. Your computer will boot into OSX. Just restart your computer and try, try again. image

8) Install bootcamp drivers. After the installation completes and you log on for the first time, open your Bootcamp_version-whatever folder you stored in the WININSTALL USB drive you created in step 2. Double-click the setup or autorun Application. Hit next-next-next If your install did not work, look over the instructions again. Though this process does not require any special skill, it is easy to mess up a step. Don’t panic. You already have a complete backup of all your data right??! Boot into Mac OSX, open Terminal, and type: diskutil list If your table does not look like mine, ask yourself, “Why self?”

This will not work with a bootleg version of Windows. Click here for an explanation.

  • Welcome to Ask Different! While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. Link-only answers can become invalid if the linked page changes.
    – grg
    Commented Feb 13, 2014 at 16:35
  • Kevin can you help me with your tutorial. I dont know what the Silver partition is for i have a 1tb external hdd i want to have windows on and a usb key with windows. So i can't find out what the silver partition is for?.
    – user71511
    Commented Feb 26, 2014 at 14:22
  • The "sliver" is created because Windows and Mac use different Boot Partition Tables. When you create that tiny sliver on your MacBook, Bootcamp re-wraps the operating systems (in a way beyond my understanding). You must create this sliver in order for the whole thing to work. This is step 1
    – Kevin
    Commented Feb 20, 2017 at 17:55

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