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My Boot Camp assistant seems to be having problems (first I get not enough space, 40 GB, etc.) which I fixed by making a partition using Disk Utility, but then I didn't get an option that others seem to get to Create a usb bootable drive for windows 7 or later. It right away asked for the ISO and started downloading Windows support software, took forever, and then said there wasn't enough space on the partition (there was).

Without Boot Camp, I tried using dd and that didn't work and just reformatting the USB drive to exFAT (FAT32 didn't seem to work, because the October 2018 update has a file over 4 GB, meanwhile I'm downloading April 2018). What happens is that once I boot up the PC, change the boot order and then select the drive, it just goes back to some VMware kernel OS that was still on it when I got the PC. I've tried running in legacy mode, secure boot is disabled.

Does anyone have any alternatives I could use?

Also I tried plugging the usb (formatted exFAT in to my mac and it seems to recognize it in the boot menu, so I'm starting to think it's something with my motherboard/bios settings).

  • I believe that if you can download an .ISO of the version of Windows you want, disk utility has a method of restoring a disk image to a drive, under Images > Scan Image for restore. have you tried that? – Steve Chambers Apr 3 at 20:47
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So, I needed to use FAT32 for my BIOS to accept it, but both the April 2018 and October 2018 updates had an install.wim file that was over 4 GB (I downloaded the English international version for both, maybe other versions are different?). So I needed to split the file. Here is how I did it for anyone else who has this problem.

I found this amazing guide for it (https://www.tenforums.com/tutorials/103340-dism-split-install-wim-file.html), but it was for Windows so I had to adapt it. I used split terminal command to split the install.wim file.

split -b 3700m /Volumes/CCCOMA_X64FRE_EN-GB_DV9/sources/install.wim install.wim

This creates install.wimaa and install.wimab. I then moved all the ISO files to the FAT32 USB, but with the new install.wim files. This time, when I booted from the USB, I get the Windows boot media, but it obviously cannot find install.wim. So I go to the command prompt and follow the guide and type out the diskpart commands it says (I followed MBR).

After that, I copied the contents of the USB drive to the Windows 10 volume that I created from the guide (I think I used xcopy, but there's other commands for it). Navigated to that volume, went to the sources folder and typed the commands:

type install.wimaa install.wimab > install.wim 

(Once that finished, I deleted the old wimaa and wimab files)

del install.wimaa
del install.wimab

After this I followed the rest of the guide, applied the image, add boot records (The disk volumes for me were different than what the guide should have given me, but that might have been a mistake on my part) and booted my pc back up after removing the USB. If it says operating system not found, this worked for me: https://www.wintips.org/fix-operating-system-was-n0t-found-error-on-windows-10-8-solved/.

This was so complicated for some reason and took me many hours to figure out.

  • You will have to return later to mark your answer as the accepted answer. – David Anderson Apr 4 at 13:50
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    The shrink value of 450 is not large enough. You are basically creating a partition that will remain empty. I would recommend a value of 800. The Dism /apply-image ... command defaults to the first image. You should use the command Dism /Get-ImageInfo ... to list all the images and choose the correct integer for /index. – David Anderson Apr 4 at 14:10
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Microsoft offers two different methods of downloading Windows. The first is a simple download of an ISO file. The second method requires the download of a MediaCreationTool1809 application which then downloads Windows and installs to a FAT32 formatted USB flash drive. Since the MediaCreationTool1809 application requires Windows to execute, you can not use this method if you are running macOS. I suppose one could install a free copy of VirtualBox, then download the ISO. After creating a Windows virtual machine from the ISO, one could download and execute the MediaCreationTool1809 application in the virtual machine to create a USB Windows installer.

The files downloaded in the ISO by the first method are not the same as the files downloaded when the second method uses the MediaCreationTool1809 application.

As you already stated in your question, the ISO contains one file that is too large to fit on a FAT32 formatted flash drive. While ExFAT formatting can solve this problem, not all PC's can boot from ExFAT formatted flash drives. (However, newer Macs can boot fro ExFAT formatted flash drives.)

The English 64 bit April 2018 update does not have any files that would not fit on a FAT32 formatted flash drive. Below is the SHA Checksum of the file I used.

$ shasum -a 256 Win10_1803_English_x64.iso
2a7e8c918347f36c23dcbab9804aca5b88eaf8b118c7356b1d96ab771ecb017f  Win10_1803_English_x64.iso
  • I tried again with the april 2018 update and it still said it was too big. – ExG Apr 4 at 0:53
  • I did not have any trouble copying to a FAT32 formatted flash drive. Perhaps your flash drive was not large enough? Or, maybe you are using a different ISO file. I updated my answer to document the file I used. – David Anderson Apr 4 at 2:30
  • I got the english international version, could that be the difference? Also the .iso file says it's 4.6gb but the install.wim is 5.3gb. Anyway I found a way to work around it, going to edit my post. – ExG Apr 4 at 12:47

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