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# How-to create bootable Windows usb flash on MacOS
- URL: https://ostreff.info/how-to-create-bootable-windows-usb-flash-on-macos/
- Published: 2024-05-18T11:24:09.000Z
- Updated: 2024-05-18T11:24:09.000Z
- Author: Jordan Ostreff
- Tags: MacOS, #Windows, #usb

First see what disks you have on your MacOS

```bash
% diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.3 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                 Apple_APFS Container disk1         500.1 GB   disk0s2

/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +500.1 GB   disk1
                                 Physical Store disk0s2
   1:                APFS Volume Macintosh HD - Data     208.3 GB   disk1s1
   2:                APFS Volume Preboot                 1.5 GB     disk1s2
   3:                APFS Volume Recovery                1.1 GB     disk1s3
   4:                APFS Volume VM                      2.1 GB     disk1s4
   5:                APFS Volume Macintosh HD            15.4 GB    disk1s5
   6:              APFS Snapshot com.apple.os.update-... 15.4 GB    disk1s5s1
```

Then insert your USB flash disk and see what is changed executing above command again:

```bash
diskutil list
```

Imagine that new disk is received device named `disk2`. Now it's time to format the usb flash drive - my recommendations is your target windows computer is older machine to use `mbr` partitions. To do this use command:

```bash
 % sudo diskutil eraseDisk FAT32 "WIN10" MBRFormat /dev/disk2
Started erase on disk2 (CCCOMA_X64FRE_BG-BG_DV9)
Unmounting disk
Creating the partition map
Waiting for partitions to activate
Formatting disk2s1 as MS-DOS (FAT32) with name WIN10
512 bytes per physical sector
/dev/rdisk2s1: 60597312 sectors in 1893666 FAT32 clusters (16384 bytes/cluster)
bps=512 spc=32 res=32 nft=2 mid=0xf8 spt=32 hds=255 hid=2048 drv=0x80 bsec=60626944 bspf=14795 rdcl=2 infs=1 bkbs=6
Mounting disk
Finished erase on disk2
```

Then you must download and install on your computer [unetbootin](https://unetbootin.github.io/?ref=ostreff.info). Using it we will write `*.iso` file to the USB disk.

![](https://ostreff.info/content/images/2024/05/image.png)

Here is the trickiest part, because on FAT32 filesystem maximum file size is 4G but actually file named `install.wim` which typically is biggest. So you must split it in pieces. Because this is special Microsoft archive file format, you need special application to do this. Download source of [wimlib](https://wimlib.net/?ref=ostreff.info) and uncompress it. Then build and install it using this:

```bash
% ./configure --without-ntfs-3g
% make
% sudo make install
```

Now you can do the following:

```bash
% wimlib-imagex split /Volumes/CCCOMA_X64FRE_BG-BG_DV9/sources/install.wim  /Volumes/WIN10/sources/install.swm 4000
Splitting WIM: 4614 MiB of 4614 MiB (100%) written, part 2 of 2
Finished splitting "/Volumes/CCCOMA_X64FRE_BG-BG_DV9/sources/install.wim"

% rm /Volumes/WIN10/sources/install.wim
```

That's all!