WinDiskWriter: Create Bootable Windows USB on Mac (Free)

Mac users who want to install Windows on a PC, Intel Mac, or virtual machine need a bootable USB drive built from a Windows ISO. WinDiskWriter handles that entire process on macOS, automatically managing bootloader setup, file splitting, and UEFI compatibility without requiring command-line work.

This guide covers what WinDiskWriter does, how to use it, which systems it supports, and how to fix common issues.

What Is WinDiskWriter

WinDiskWriter is a free, open-source macOS utility developed by TechUnRestricted. It writes Windows ISO files to USB drives and makes them bootable under both UEFI and Legacy BIOS modes.

The app targets Mac users who need Windows installation media but lack a native graphical tool to create it. It runs on macOS versions ranging from OS X Snow Leopard 10.6 all the way through macOS Tahoe 26.0, and the developer provides separate builds for Intel (x86_64) and Apple Silicon (ARM64) machines.

The software uses wimlib to handle Windows Image (WIM) files and optionally uses grub4dos to enable Legacy BIOS boot support.

Key Features

Automatic install.wim splitting: FAT32 limits individual file sizes to 4 GB. Newer Windows ISOs include an install.wim file that exceeds that limit. WinDiskWriter detects the oversized file and splits it into smaller .swm fragment files automatically. The Windows installer recognizes the split and continues the installation normally.

UEFI and Legacy BIOS support: The app creates USB drives that boot under both modern UEFI firmware and older Legacy BIOS systems. This covers PCs with older hardware that cannot boot from UEFI-only drives.

EFI support for Windows Vista and 7: Windows Vista and 7 do not support EFI booting natively. WinDiskWriter extracts an EFI-capable bootloader from the installer and adds it to the USB drive during the write process.

Windows 11 requirement bypass: Before writing, you can enable the Patch Installer Requirements option. This bypasses TPM, Secure Boot, and minimum RAM checks that Microsoft enforces for Windows 11.

Built-in verification: The app checks the ISO file integrity before writing begins, reducing the risk of a corrupted bootable drive.

Multi-format support: WinDiskWriter supports ISO, IMG, WIM, and other common image formats.

Supported Windows Versions

WinDiskWriter supports the following Windows versions for both UEFI and Legacy boot modes:

• Windows 11 (x64)
• Windows 10 (x64, x32)
• Windows 8.1
• Windows 8
• Windows 7
• Windows Vista

Supported macOS Versions

Versions Mac OS X Lion 10.7 and Snow Leopard 10.6 are not officially verified but should work.

How to Use WinDiskWriter

Step 1: Download WinDiskWriter

Visit the official WinDiskWriter page and download the latest release (Version 1.3 as of January 2026). Choose the correct build for your Mac: Intel or Apple Silicon. The app weighs approximately 852 KB and requires no additional runtime installations.

Step 2: Prepare a Windows ISO

Download the Windows ISO directly from Microsoft. WinDiskWriter cannot repair a corrupted or incomplete source file, so always use an official, verified ISO. If you plan to install Windows 11 on hardware that does not meet Microsoft’s minimum requirements, keep the Patch Installer Requirements option in mind before writing.

Step 3: Insert Your USB Drive

Connect a USB drive with enough capacity for the Windows image (at least 8 GB for most Windows versions). WinDiskWriter will format the drive during the write process, so move any important data off it before proceeding.

Step 4: Open WinDiskWriter and Select the ISO

Launch WinDiskWriter and select your Windows ISO file. The app reads the image and determines the correct write method based on the Windows version inside.

Step 5: Select the Target USB Drive

WinDiskWriter detects connected USB drives and lists them as destination targets. Select your USB drive from the list.

Step 6: Configure Options (Optional)

• Enable Patch Installer Requirements if you need to bypass Windows 11 hardware checks.
• Enable Legacy BIOS Support if the target PC uses older firmware that does not support UEFI.

Step 7: Start Writing

Click Start. WinDiskWriter formats the USB drive as FAT32, writes the image data, applies any patches you selected, and splits the install.wim file if it exceeds 4 GB. A progress indicator shows the status throughout.

Step 8: Verify and Boot

After writing, WinDiskWriter runs a verification pass to confirm the drive is correctly written. Insert the USB drive into the target PC, set the BIOS or UEFI to boot from USB, and start the Windows installation.

WinDiskWriter Troubleshooting Guide

USB Drive Not Detected

Disconnect the USB drive and reconnect it to a different port. If the drive still does not appear, open Disk Utility on your Mac to confirm the system recognizes it. Drives formatted with uncommon or corrupted partition tables sometimes fail to show up in WinDiskWriter even when macOS detects them.

Write Process Fails Midway

A failed write usually points to a corrupted ISO or a failing USB drive. Download a fresh copy of the Windows ISO from Microsoft and verify the SHA-256 checksum before retrying. If the issue persists with a different ISO, test the USB drive with a disk health tool to rule out hardware failure.

Computer Will Not Boot from USB

Enter the target PC’s BIOS or UEFI firmware settings and confirm USB is set as the first boot device. On UEFI systems, also check whether Secure Boot is enabled. Some older PCs require you to press a boot menu key (commonly F12, F11, or Esc) at startup to select the USB manually.

If the PC uses Legacy BIOS and the drive does not boot, re-create the USB in WinDiskWriter with the Legacy BIOS Support option enabled.

Write Speed Is Very Slow

Slow write speeds typically point to the USB drive itself rather than WinDiskWriter. USB 2.0 drives write at significantly lower speeds than USB 3.0 drives. Use a USB 3.0 or 3.1 drive connected to a USB 3.0 port on your Mac for the fastest results.

Access Denied Error

macOS may block WinDiskWriter from accessing the USB drive if it lacks the required disk permissions. Open System Settings, go to Privacy and Security, then Full Disk Access, and add WinDiskWriter to the list.

ISO File Appears Corrupted

Re-download the ISO directly from Microsoft’s official website. After downloading, compare the file’s SHA-256 checksum against the value Microsoft publishes. A mismatch confirms the download is corrupted and requires a fresh download.

WinDiskWriter Limitations You Should Know

WinDiskWriter formats destination drives as FAT32 only. It does not offer exFAT or NTFS formatting options. This means large install.wim files always require splitting, and the app handles that automatically rather than offering you an alternative format.

The app also does not support creating media for operating systems other than Windows. For Linux ISOs, you need a different tool such as UNetBootin or Balena Etcher.

Long-term macOS compatibility depends on the developer’s update schedule. As an open-source project maintained by an individual developer, future macOS releases may introduce compatibility gaps before a patch becomes available.

Related Guides

• How to Use Ventoy to Create a Bootable Windows 11 USB Drive
• How to Use Rufus to Create a Bootable USB Drive on Windows
• How to Create Bootable Windows 11 26H2 USB Install Media (Rufus, Ventoy, CMD)

Frequently Asked Questions