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Migrate Windows 8 or higher to an External Drive

IMPORTANT: This article is a guide only. Apple requires that Windows be installed on your internal hard disk: http://support.apple.com/en-us/HT201456

This Article Covers

  1. Introduction
  2. Migration Scenarios
  3. System Requirements
  4. Prepare External Drive in OS X using Disk Utility
  5. Disk Utility Setup
  6. Partitioning the Drive
  7. Migration with Winclone
  8. Conclusion
  9. Troubleshooting 


Windows 8 now installs in EFI mode for computer hardware that supports EFI. Recent generations of PCs as well as Macs are capable of running Windows 8 in EFI mode, which speeds boot time compared to BIOS (legacy) mode. The technical aspects of EFI mode and legacy mode are beyond the scope of this document.

The implications of EFI mode for newer Macs running Windows 8 in Boot Camp are nearly unlimited storage location and migration options. 

 Please also see this article for videos and additional considerations for running Windows from an external drive.

Storage and Migration Scenarios back to top ^

  • Migrate Boot Camp from internal to external bootable drive
  • Run multiple bootable Windows 8 partitions on internal Intel Mac drive
  • Run multiple bootable Windows 8 partitions on external drive attached to Intel Mac
  • Migrate Windows 8 from a PC to Intel Mac
  • Migrate Windows 8 from Boot Camp to a PC that supports EFI mode
  • Create Winclone image of a Windows 8 PC drive
  • Restore a Windows 8 Winclone image to a PC drive for use in a PC that supports EFI mode

System Requirements back to top ^

In order to move your Bootcamp partition from your Mac to an external drive, it must meet the following requirements:

  1. Intel Based Mac with EFI version 2 or greater (see http://support.apple.com/kb/HT1237)
  2. USB or Thunderbolt External drive (USB Flash drives not supported)
  3. Bootcamp partition with Windows 8 or Windows 8.1 installed

Prepare External Drive in OS X using Disk Utility back to top ^


Before migrating Windows 8 Boot Camp to a bootable external drive, the drive must be formatted with the GUID partition scheme and partitioned with a MS-DOS (FAT32) partition. Keep in mind that this process will erase all existing data on the external drive, so make sure to back up any critical data elsewhere before proceeding.

Attach the external drive and open Utilities-> Disk Utility.

Select the external drive in the left side column. At the bottom of the Disk Utility window will be information about the disk. If the Partition Map Scheme is already set as “GUID Partition Table” you may skip to the section below “Create the Destination Partition”. If the Partition Map Scheme is anything other than “GUID Partition Table”, proceed to the section “Erase Disk”.

Disk Utility Setup back to top ^


  1. Make SURE the external drive (and not the volume) is selected
  2. Click the Partition tab in Disk Utility and in the drop down menu under Partition Layout, select "1 Partition". If you need other partitions in addition to the Boot Camp partition, you should create them now. You may also resize the Boot Camp partition and leave free space for later adding additional partitions.
  3. Click on the box under the Partition Layout drop down menu to select it.
  4. Enter a name for the partition and set the format to "MS-DOS (FAT)". You may also change the selected size by entering a number in GB. In our example, we will leave the Size to utilize all available space on the drive for a single MS-DOS (FAT32) partition.
  5. Click Options to set the Partition Map Scheme to GUID Partition Table.

Partition Drive back to top ^

Select the GUID Partition Table option and click OK. The next step is to click Apply, which will erase all existing partitions and data and create a new partition table. Click Apply to accept the changes and create the new partition table.

A Note About File System Formats

At this stage you may be wondering "Why did we just create a MS-DOS (FAT32) partition when Windows 8 uses NTFS format?"

The reason for creating a MS-DOS (FAT32) partition as the destination for the migration is required because Disk Utility cannot natively create NTFS formatted partitions. Winclone will overwrite the MS-DOS (FAT32) format during the migration and the result will be a NTFS formatted Windows file system.

Migration with Winclone back to top ^

Once the partition has been created in Disk Utility, you may quit out of Disk Utility. Verify that the newly created partition is visible as a mounted volume on the Mac desktop. Open Winclone and select the current internal drive's Boot Camp partition in the Sources column. Or, if you have a Winclone image that will be used as the source for the migration, chose the Winclone image file in the Sources column. Select the new external drive MS-DOS (FAT32) volume as the Destination. Click the "Restore to Volume" button to begin the migration process.

Conclusion back to top ^

Once the migration process is complete, open System Preferences -> Startup Disk. The new external drive should appear along with the OS X volume (and internal Boot Camp volume if it exists) and can now be selected as the startup volume. Optionally, restart while holding the Option key and the new external Boot Camp volume will be available for startup.

Troubleshooting back to top ^

IMPORTANT: Neither Apple or Winclone support running Windows on an external drive. We will provide a refund for Winclone if you can't use it to complete your desired migration and are unsatisfied. 

This page may be helpful (includes USB drive information): 

  1. If you successfully restore your image to your external partition and experience any start up errors, please try changing the boot mode to EFI and legacy and reboot.
  2. In Winclone, hold the Control and Option keys and select the Boot Camp partition in the context menu. Select "Make legacy bootable", then reboot to Windows.
  3. If the result is the same as before, boot back into OS X and again hold Control Option, select Boot Camp and set "Make EFI bootable", then restart into Windows.
  4. If "Make EFI Bootable" does not appear, please temporarily set your System Language to english. 

Multiple Boot Camp Partitions Present on System

  • Multiple Windows systems present at boot time can cause unexpected problems, especially when the systems are exact clones. Windows will assign the boot drive letter based on what it detects on the various buses. Your internal drive's Boot Camp will likely remain assigned to C:, but your external drive will probably be assigned D: or E:.
  • It is also advisable to reassign letters for all external drives in case they don´t appear in My Computer/ Devices and Drives via Control Panel /Administrative Tools/ Computer Management/ Storage/ Disk Management.
  • Normally this isn't an issue, but some third-party Windows applications that initialize files during startup specify an absolute path (i.e. C:/Windows/System 32/drivers/..etc). Since the externally attached Windows is booting as D:/Windows/System 32... this can cause problems.



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