When installing Windows on UEFI-based PCs using Windows Setup, your hard drive partition style must be set up to support either UEFI mode or legacy BIOS-compatibility mode.

For example, if you receive the error message: , it’s because your PC is booted in UEFI mode, but your hard drive is not configured for UEFI mode. You’ve got a few options:

1. Reboot the PC in legacy BIOS-compatibility mode. This option lets you keep the existing partition style. For more info, see Boot to UEFI Mode or Legacy BIOS mode.

2. Configure your drive for UEFI by using the GPT partition style. This option lets you use the PC’s UEFI firmware features.

   You can preserve your data and convert the drive using the MBR2GPT tool, or you can choose to reformat the drive using the instructions below. Reformatting will erase all the data on the drive.

Many PCs now include the ability to use the UEFI version of BIOS, which can speed up boot and shutdown times and can provide additional security advantages. To boot your PC in UEFI mode, you'll need to use a drive formatted using the GPT drive format.

Many PCs are ready to use UEFI, but include a compatibility support module (CSM) that is set up to use the legacy version of BIOS. This version of BIOS was developed in the 1970s and provides compatibility to a variety of older equipment and network configurations, and requires a drive that uses the MBR drive format.

However, the basic MBR drive format does not support drives over 4TB. It's also difficult to set up more than four partitions. The GPT drive format lets you set up drives that are larger than 4 terabytes (TB), and lets you easily set up as many partitions as you need.

1. Turn off the PC, and put in the Windows installation USB key or DVD.

2. Boot the PC to the USB key or DVD in UEFI mode. For more info, see Boot to UEFI Mode or Legacy BIOS mode.

3. In Windows setup, When choosing an installation type select Custom.

4. On the Where do you want to install Windows? screen, select each of the partitions on the drive where you're installing Windows, and select Delete. The drive will show a single area of unallocated space.

5. Select the unallocated space and click Next. Windows detects that the PC was booted into UEFI mode, and reformats the drive using the GPT drive format, and begins the installation.

1. Turn off the PC, and put in the Windows installation DVD or USB key.

2. Boot the PC to the DVD or USB key in UEFI mode. For more info, see Boot to UEFI Mode or Legacy BIOS mode.

3. From inside Windows Setup, press Shift+F10 to open a command prompt window.

4. Open the diskpart tool:

5. Identify the drive to reformat:

6. Select the drive, and reformat it:

7. Close the command prompt window.

8. Continue the Windows Setup installation.

   When choosing an installation type, select Custom. The drive will appear as a single area of unallocated space.

   Select the unallocated space and click Next. Windows begins the installation.

To automate this process, you'll need to run Windows Setup from Windows PE and use a script to detect which mode you’re in before installing Windows. For more info, see WinPE: Boot in UEFI or legacy BIOS mode.