Create a windows installation USB with two partitions

make_mbr.ps1

#Requires -RunAsAdministrator
param(
    [String]$image=(Join-Path $PSScriptRoot "Win10_2004_EnglishInternational_x64.iso"),
    [Switch]$update
)
If ( -Not $update.IsPresent) {
    If ( -Not (Test-Path $image)) {
        Write-Host "Error: <image> not found"
        Exit 1
    }

    $drives = Get-Disk | Select-Object -Property Number,FriendlyName
    Write-Host "Available Devices"
    $drives | ForEach-Object {
        Write-Host ("{0} : {1}" -f $_.Number.toString().PadLeft(2), $_.FriendlyName)
    }
    $choice = Read-Host -Prompt "Selection"

    If ($choice -match "^[\d\.]+$") {
        If ( (Read-Host -Prompt "Confirm Selection") -ne $choice) {
            Write-Host "Error: Failed to Confirm Selection"
            Exit 1
        }
    } else {
        Write-Host "Error: Invalid Selection"
        Exit 1
    }

    [int]$choice = $choice

    $gpt = $true

    If ( (Get-Disk | Where-Object { $_.Number -eq $choice}).PartitionStyle -eq "MBR" ) {
        $gpt = $false
    }

    $partition = Join-Path $PSScriptRoot "partition.txt"

    If (Test-Path $partition -PathType Leaf) { Remove-Item $partition -Force | Out-Null }

    New-Item -Path $PSScriptRoot -Name "partition.txt" -ItemType File | Out-Null

    Add-Content -Path $partition -Value "select disk $choice"
    Add-Content -Path $partition -Value "clean"
    If ( $gpt -eq $true ) {
        Add-Content -Path $partition -Value "convert mbr"
    }
    Add-Content -Path $partition -Value "create partition primary size=1024"
    Add-Content -Path $partition -Value "format quick fs=fat32 label=""USB-BOOT"""
    Add-Content -Path $partition -Value "assign"
    Add-Content -Path $partition -Value "create partition primary"
    Add-Content -Path $partition -Value "format quick fs=ntfs label=""USB-INSTALL"""
    Add-Content -Path $partition -Value "assign"
    Add-Content -Path $partition -Value "exit"

    Write-Host " > Repartitioning Disk"

    diskpart /s $partition | Out-Null

    Remove-Item $partition -Force | Out-Null

    $install = $null
    $boot = $null

    $count = 0

    While (($null -eq $install) -or ($null -eq $boot)) {
        Write-Host " - Waiting for Disk"
        Get-Volume | ForEach-Object {
            If ($_.FileSystemLabel -eq "USB-INSTALL") {
                $install = ("{0}:" -f $_.DriveLetter)
            }
            If ($_.FileSystemLabel -eq "USB-BOOT") {
                $boot = ("{0}:" -f $_.DriveLetter)
            }
        }
        If ($count -gt 10) { break } else { $count = $count + 1 }
        Start-Sleep -Seconds 2
    }

    If (($null -eq $install) -and ($null -eq $boot)) {
        Write-Host "Error: cant not find <USB-BOOT> or <USB-INSTALL>"
        Exit 1
    }

    Write-Host " > Updating Boot Sector"

    bootsect.exe /nt60 $boot | Out-Null

    $iso = "{0}:" -f (Mount-DiskImage -ImagePath $image -PassThru | Get-Volume).DriveLetter

    Write-Host " > Copying <USB-BOOT> Files"

    $excludes = "sources"
    Get-ChildItem -Path $iso | Where-Object{$_.Name -notin $excludes} | Copy-Item -Destination $boot -Recurse -Force | Out-Null
    New-Item -Path $boot -Name "sources" -ItemType Directory | Out-Null
    Copy-Item -Path (Join-Path (Join-Path $iso "sources") "boot.wim") -Destination (Join-Path $boot "sources") | Out-Null

    Write-Host " > Copying <USB-INSTALL> Files (slow)"
    
    $excludes = @("install.wim", "install.esd")
    Get-ChildItem -Path $iso -Recurse -Exclude $excludes | Copy-Item -Destination { Join-Path $install $_.FullName.SubString($iso.length) } -Force | Out-Null

    Write-Host " > Copying <install.wim> to <USB-INSTALL> (slow)"
    Copy-Item -Path (Join-Path $PSScriptRoot "install.wim") -Destination (Join-Path $install "sources") | Out-Null
} else {
    $install = Get-Volume | Where-Object { $_.FileSystemLabel -eq "USB-INSTALL" }
    If ( ($install | Measure-Object).Count -eq 1) {
        $install = "{0}:\" -f $install.DriveLetter
    } else {
        Write-Host "Error: cant find <USB-INSTALL>"
        Exit 1
    }
    Write-Host " > Copying <install.wim> to <USB-INSTALL> (slow)"
    Copy-Item -Path (Join-Path $PSScriptRoot "install.wim") -Destination (Join-Path $install "sources") -Force | Out-Null
}

Write-Host "Complete."

to use this script you need:

• windows iso
• modified install.wim (made from the file in the iso)
• this script (optionally updating $image with the name of your iso)

place all files in the same folder and execute the script from an elevated powershell prompt.

the script takes two parameters, both optional.
$image : an absolute path to your iso
$update : if you have already configured the partitions, this will only copy install.wim.