Guide to Dual Booting Windows Without Repartitioning

Introduction

• Dual boot two different versions of Windows without installing an extra hard drive or repartitioning.

Traditional Dual Boot Methods

• Installing a second hard drive or partitioning the existing drive, both of which have downsides like cost and capacity issues.

Alternative: Using Virtual Discs

• Utilize virtual discs to run multiple Windows installations on one hard drive without repartitioning.
• A virtual hard drive is essentially a file that can be mounted as a hard drive, suitable for backups and installing a Windows copy.

Steps to Install Windows on a Virtual Hard Drive

Required Tools

• A USB drive with a Windows installation (e.g., Ventoy drive).

Creating a Virtual Hard Drive

1. Open Disk Management: Navigate to Action > Create VHD.
2. Select Location: Store the virtual hard drive file, e.g., C:\Vdisk.
3. Name and Size: Create a virtual hard drive file without spaces, and choose size (dynamic expansion recommended).

Installing Windows

1. Boot from the Windows setup USB.
2. Open a command prompt with Shift + F10.
3. Use diskpart to attach the virtual disk:

   select vdisk file=C:\Vdisk\Windows10.vhdx
   attach vdisk
   

4. Refresh the Windows setup screen to detect the new drive.
5. Complete the installation normally.

Post-Installation Configuration

Setting Default Operating System

• Use the boot manager or msconfig to set boot preferences and timer.

Renaming Boot Entries

• Edit the boot configuration using bcdedit to change names for easy differentiation.

Resizing the Virtual Disk

• Navigate dispart in the command prompt and specify the new size using the expand vdisk command.

Manual Boot Entry Configuration

• Use bcdedit to manually add or modify boot entries:
  • Copy existing entries.
  • Modify path and device entries for the virtual drive.

Tips and Considerations

• Always backup your BCD before making changes.
• Expanding virtual drives is straightforward; shrinking is more complex.
• The setup relies on a primary OS (Windows 11 in the example) and losing it may compromise the virtual instances.
• Regularly back up virtual drives for safety.

Troubleshooting

• If BCD editing goes wrong, rebuilding the UEFI bootloader is an available fix.

This guide provides a streamlined approach to managing multiple Windows environments without altering physical hardware partitions, utilizing the flexibility of virtual hard drives.