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).

Double click on the .ISO file. This will mount the installation disk onto a drive (in my case, letter E).
Plug the SSD drive onto a spare USB port
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.

Enjoy!

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

Posted on Jun 10, 2016 1:48 AM

38 replies

Dec 10, 2016 10:10 AM 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 10:18 AM 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.

Csound1

Level 9

60,063 points

Dec 10, 2016 11:14 AM in response to Digitalclips

Only OS X values can boot OS X, eXfat is a Microsoft format, so it is not compatible with booting the system.

Dec 11, 2016 7:59 AM 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.

DavidB02

Level 1

4 points

Dec 21, 2016 2:23 AM 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?

shokol8

Level 1

10 points

Feb 3, 2017 12:46 PM in response to LFGL

QQuick format didn't work for me, should I just type "format" then?

Jul 31, 2017 9:31 PM in response to LFGL

I do not understand the double click on the .iso file. It just leads me to burning a disk. Where do I find "E:\sources\install.esd" ? There is something missing here. --DKH

Loner T

Level 9

59,536 points

Oct 28, 2017 10:48 AM in response to Valent1no

I suggest running BC Assistant and using the drivers that are available from Apple. If you use this method, please post the Product Version (not the full XML) from Bootcamp.xml.

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