A boot disk (sometimes called a startup disk) is a media file that contains startup files that your computer can use to boot up, in case the Operating System of your computer becomes corrupt or unusable.
Recovery media (WinRE) can be used to restore a Windows device to the Working state, even if the user needs to replace the hard drive or completely wipe the drive clean.
You would need to create the Windows RE bootable media in X64 or X86 environment depending on the OS architecture you are restoring.
For creating Windows image, follow the steps below or learn more here.
Note: Windows image can be downloaded from the Microsoft website: (Sample link):
Step 1: Install and open the deployment and imaging tools environment
Step 2: Extract the Windows RE image from the Windows image
Once image is mounted, copy 'install.wim' from 'G:\sources\' to 'D:\ sources' , where G is the ISO mounted drive:
Dism /Mount-Image /ImageFile:D:\sources\install.wim /Index:1 /MountDir:C:\mount\Windows\
where D is the location where install.wim is present.
Copy the Windows RE image:
xcopy C:\mount\Windows\Windows\System32\Recovery\winre.wim C:\Images\winre.wim /h
Unmount the Windows image:
Dism /Unmount-Image /MountDir:C:\mount\Windows\ /Discard
Step 3: Create a working folder for Windows RE files
Step 4: Add the Windows image
Step 5: Create bootable USB flash drive