Looks like no one’s replied in a while. To start the conversation again, simply ask a new question.


Question: Run Windows 10 from an external SSD disk? Yes, it works!

This is what I have done to make it work. The whole process takes approximately, 45 minutes but I think it is really worth it if you want to run a fast and clean installation of Windows 10 on your iMac.

What you need:

  • An external SSD disk - Data will be erased ⚠
  • An iMac 27" (Late 2013 in my case)

Temporarily, for the installation, you will also need:

  • A running computer with Windows 7, 8 or 10 to copy the right files onto the SSD disk and make it bootable
  • A running computer with OS X to download the BootCamp software
  • A USB thumb drive - Data will be erased ⚠

First, in Windows, get yourself an ISO file of Windows 10. You can use the Media Creation Tool provided at https://www.microsoft.com/en-gb/software-download/windows10 and choose to save it as an ISO file (do not create a bootable USB media).

  1. Double click on the .ISO file. This will mount the installation disk onto a drive (in my case, letter E).
  2. Plug the SSD drive onto a spare USB port
  3. Open a Administrator command prompt and type:
    1. diskpart
    2. list disk (identify the number of your external SSD drive)
    3. select disk 2 (or another number for your external SSD disk, be careful not to wipe your internal disk, usually on 0).
    4. clean - Be careful, if you have selected the wrong disk, it will erase all the data on it
    5. create part pri
    6. format quick
    7. assign letter=Y (or another letter if already used)
    8. active
    9. exit
    10. dism /apply-image /imagefile:"E:\sources\install.esd" /index:1 /ApplyDir:Y:\(change E to another letter for the mounted ISO file)
    11. BCDBOOT.EXE Y:\WINDOWS /S Y: /F BIOS (this will make the drive bootable in BIOS only (not EFI)
    12. exit
    13. Eject all drives cleanly or simply shut down your PC.

Secondly, on your Mac, open BootCamp assistant (click on Launchpad and type "bootcamp" to find it) and ONLY tick "Download the latest Windows support software from Apple". Save it all on your USB thumb drive. Shut down your iMac. Remove the USB thumb drive and keep it in your hand.

Power up your iMac by pressing the option key (alt). You will see an orange icon with Windows. Select this and wait until you see "Getting devices ready", wait a little bit longer until you hear the startup chime and press the option key (alt) again to make sure you boot on the external drive. That's it!

Now you have a copy of Windows running from your external USB drive. You just need to install the BootCamp drivers on your USB thumb drive (\Bootcamp\Setup.exe). Reboot.

That's it, you've got Windows 10 running natively on your beautiful iMac.


iMac (27-inch, Late 2013), Windows 10, null

Posted on

Question marked as Solved

The reply is in the answer. I do not know how to post a tip!

Posted on

Jun 10, 2016 6:06 AM in response to LFGL In response to LFGL

I've posted this before but in less detail: This for Mac folks not familiar with using Windows commands (or would rather not). This is all done on the Mac until you actually boot into your new Windows USB.

For anyone with Parallels or VMWare Fusion it is extremely simple too. Get two free apps for Windows (I used the Mac to get them and download, to avoid crapware and then transferred the .exe once unzipped on the Mac to the Parallels.) The two apps are WintoGo (free) which uses an ISO of Windows 10 (or 8.1) to transfer to your USB3 attached external. I use an SSD and a $10 cable from Amazon. The other app you need to set up the drive without needing any knowledge what-so -ever about Bios etc. is called MiniTools Partition (free version) which allows you from Parallels to set the USB disk to MRB (essential) then partition the drive for the WintoUSB installation. Mac users are not familiar with all this stuff but two are required and it is like using Mac's own Disk Utils. You make two partitions, one small one, I use 200 MB (note that's MB not GB) and format as Fat32. Then the rest as NTSF. You then set the Fat32 partition as Primary and active then the NTFS one as active too. It all sounds complicated but it isn't really. All the options are simply there in the menus. The big difference with MiniTools Partition compared to Apple Disk Untilitiesis that it gets a little 'getting used to' in that every time to select an action, such as partition the 200 MB area, until you click the 'Apply' button nothing happens. If you do a few selections then click 'Apply' it does them sequentially. I prefer to apply each one as I go as sometimes options are not available unless the previous one is applied, e.g. you can't make a partition primary until it is formatted and so on.

I have several SSDs made this way and find a paid for utility on the Mac worth the $20, NTFS for Mac. This allows tou to mount multiple Windows bootable disks on the Mac desk top and have full read and write access. This means you can copy programs and data between then using the Finder on the Mac and not have to deal with Windows. I copy my entire Steam folder over for example. This saves hours of re-downloading.

Lastly AMD in May 2016 released Crimson Drivers for Macs running Windows. On my new Mac Pro I get full double GPU performance with AMD Catalyst now.


Install this before anything else.

BTW I add a tild ~ in front of the AMD drivers folder in Bootcamp drivers (to prevent them even trying) if I install them later, as well as the Realtech driver folder. they both suck at time of writing. Windows installs better drivers itself. The only Apple drivers I use are the ones for the Apple keyboard. I bought a three button mouse too.

Jun 10, 2016 6:06 AM

Reply Helpful

Oct 14, 2016 6:13 AM in response to nrkeone In response to nrkeone

It may sound like 13 steps is a pain but I can do the entire process in under ten minutes and be up and running. Yes I tried WinClone, it took hours and the copy of Boot Camp failed not to mention it took a while to create the Boot Camp and partitioning my internal for Windows is not something I like doing. I have never had a failure once using WintoUSB from Parallels and it is incredibly fast using external SSDs over USB3. I just made a new one yesterday as it happens as Windows itself started acting up by refusing an update as "I wasn't using an officially sanctioned USB drive". So I simply started over from scratch from my genuine Windows 10 ISO and ten minutes later had a fully working updated Windows 10 (I'd love to know why after six months Microsoft suddenly decided to check if it was an official USB drive and then why it doesn't on installation). I stress all my external installations are digitally certified as Genuine every time as I always use the same Mac Pro I paid for and registered with Microsoft.

Using Paragon's NTFS extension on my Mac I can mount two Windows active boot drives together and use the Mac's Finder to copy folders over from one to the other. In my case it's the Steam Folders. That doesn't take long either given I have a ton of games including GTA V. Re downloading from Steam would take ages. I just reinstall Steam again so it is verified and the first time you run GTA V it installes DirectX etc.

I suspect the only area non Windows aware folks will have issues is using Mini Tools to prepare a disk. Not that it is hard but you have to know how to create two partitions (I format first in Mac using Utilities then wipe in Minitools from parallels and recreate the two partitions) and know to make them both Primary and the smaller EFI one Active. Once you learn how to do this it is easy and takes two minutes.

Oct 14, 2016 6:13 AM

Reply Helpful

Oct 14, 2016 6:18 AM in response to LFGL In response to LFGL

"A running computer with OS X to download the BootCamp software"

Not needed, Bootcamp is part of OS X, no download required,

Seems like a lot of work just to get the dubious honor of running windows. Simpler just to buy one, and doesn't pollute your Mac.

Oct 14, 2016 6:18 AM

Reply Helpful

Dec 9, 2016 8:32 AM in response to LFGL In response to LFGL

Is this h/w dependent? I have a MacBook Air. The procedure goes OK, but when I try to boot the external SSD I get a white-on-black text screen telling me that my boot configuration file is missing or damaged. I've tried many of the "how-to" procedures out there unsuccessfully. Many posts say "you can't boot Windows 10 off an external drive" but then I see posts where plenty of folks have.

Dec 9, 2016 8:32 AM

Reply Helpful

Dec 9, 2016 9:08 AM in response to bediddleby In response to bediddleby

Nope not hardware specific (within reason), I can boot to an external SSD from any of my Macs. The problem is most likely you did in incorrectly. It's mind blowingly easy once you know (like most things.) But tricky first few times.

OK How to with screen shots:

This all assumes you are running Parallels or VMWare with an SSD already formatted on the Mac as ExFat as a single volume. You dismount the SSD in the Mac Finder and re attach with Parallels running (Windows 10) and select parallels for the SSD to mount in.

User uploaded file

The trick is setting up the SSD using a free utility on the Parallels side (i.e. it's a Windows app) called miniTools Partition Free: https://www.partitionwizard.com/free-partition-manager.html

I downloaded on the Mac then dragged to Parallels. Then learn how to use this very clever utility.

You delete the SSD, then Create a new 200 MB partition as Fat32, set to Primary (Not Logical) and Active. Once done create another partition set to NTFS and Primary using all the remaining space. Sounds easy but takes a while to fathom out the interface I know. Once you do it's as easy as Disk Utilities.

User uploaded file

Now you can move to the next step. You need a genuine Windows 10 ISO (The Anniversary version is available at Microsoft) https://www.microsoft.com/en-us/software-download/windows10ISOAgain I download the ISO on Mac and drag to Parallels desktop. I bought on Amazon and this gave me a digital registration tied to my Mac on which I did the first installation. Great thing is as many SSDs I make they all automatically get activated as genuine. Do not try to get around this, Microsoft are good and screwing with the installation after a very short time of you don't have a legit activation code.

Next obtain WintoUSB free version. https://www.microsoft.com/en-us/software-download/windows10ISO Again I download on Mac and drag to Parallels Desktop

Run WintoUSB, select the ISO and then the destination disk, you will see this if you correctly set up the SSD in miniTools Partition:

User uploaded file

Check the EFI (FAT32 small partition) as the system partition then the larger NTFS as the boot partition as shown above. Don't forget the extra step of making the small partition 'Active in miniTools Partition.

Click Next and in my case over USB3 and a 256 GB SSD it takes about ten minutes to complete. Shut down Mac and reboot with option held and select EFI and start the procedures as per normal (several restarts).

I have Paragon's NTFS extension on my Mac.


User uploaded file

This is so I can, once Windows is finally installed, I quit it and reboot to the Mac. The Paragon extension allows me to drag anything I want into my Windows SSD (I use user/myname/downloads) just as a protocol I've adopted for things like zip extractors and BootCamp Drivers.

I also can mount earlier made Windows SSDs in the Finder and drag entire installations such as Steam folder out of Program Files (86) etc. from one SSD to the other (to the same place obviously) and happily work away on my Mac as this is being done, no need to do anything in Windows.

This is the installed Windows 10 volume seen in the Mac's Finder.

User uploaded file

It all seems tricky but once you master MiniTools Partition is is a walk in the park. I can do all of the above in half an hour including copying over my Steam and user data from a previous set up SSD.

Dec 9, 2016 9:08 AM

Reply Helpful

Dec 10, 2016 10:10 AM in response to Digitalclips In response to Digitalclips

The closest I've come is to get it to attempt booting. I get the Windows "window" logo and spinning white wheel that is typical on bootup. But after about 20 seconds, I get a blue screen with "INACCESSIBLE BOOT DEVICE" as the error. I've tried at least 6 different methods and cannot get Win10 Pro 64 to boot externally. It works fine if I partition my internal hard drive and boot that. I believe I'm giving up!

Dec 10, 2016 10:10 AM

Reply Helpful

Dec 10, 2016 10:18 AM in response to bediddleby In response to bediddleby

Did you create the external SSD on the same Mac? Is is the SSD a USB3? Just a few thoughts.

Did the install go very fast? If slow then it could be a formatting issue. I found SSDs recently would not format with ExFat on the Mac at the start without two attempts then the whole process failed to boot like you, and I noticed WintoUSB took far longer than normal. I used the inbuilt format that comes with the Paragon Mac extension and tried again and all was well. This is a recent thing with macOS Sierra for me but I am using Developer releases so it could just be these with that issue.

Dec 10, 2016 10:18 AM

Reply Helpful

Dec 11, 2016 7:59 AM in response to Digitalclips In response to Digitalclips

Yes, everything's been done on the same Mac. It is a USB3 SSD drive. I'd say the time was about what I'd expect. I believe we're talking about two different methods, though. I'm not using Parallels or VMWare. I have a regular Windows partition on my internal HD I boot from and used the original poster's method (among others found on various forums.) All used Windows running natively on my Mac to create Windows on the SSD. It's formatted with NTFS, not ExFat.

Dec 11, 2016 7:59 AM

Reply Helpful

Dec 21, 2016 2:23 AM in response to Digitalclips In response to Digitalclips

I am trying to boot from an external USB drive (NTFS) containing a full installation of Windows 10 on my Macbook pro running OS-X Sierra. However, when I start the system and hold the option key only the internal disk is shown and the option to net boot, no USB device is shown. The external USB drive boots successfully from a Linux PC and a Windows laptops and Windows 10 starts successfully.

Unfortunately, I am new to Macs & OS-X and am unable to get the external windows disk to work. Do you have any suggestions on how to get an existing external USB drive running Windows 10 to boot successfully on a Macbook. Or do I have to reinstall Windows 10?

Dec 21, 2016 2:23 AM

Reply Helpful
User profile for user: LFGL

Question: Run Windows 10 from an external SSD disk? Yes, it works!