What you did here is correct. Whether you want to install Windows with GPT or MBR, you should leave the partition unallocated so that Windows installation will create all necessary partitions.
There are 2 things you need to know if you want to install Windows using GPT partition scheme:
Set your BIOS for UEFI. Some BIOS will have an option such as UEFI or MBR, some will have option as CSM. With CSM disabled, you are using UEFI, with CSM enabled, you are using MBR.
When booting Windows installation, There are 2 options to select from DVD/USB installation disk:
One prefixed with UEFI-USB and the other is just plain USB. Same as for DVD Attachment 95222
Once the installation USB/DVD is booted. Based on what you select from the boot menu, windows will determine what type of installation you want to install. Click Customize, select the unallocated partition, click next to let Windows installation creates all needed partitions (Do not format) and set the Partition type correctly.
Continue with the installation.
I'm pretty savvy with Partition Management & dual/ multi booting since Win 95/98/ NT days, partition table editing, VHD native boots, BCDboot etc and the UEFI vs BIOS install / boot in a Mixed OS scenario still messes with me. I need to do some intensive Re-reading to debug issues I'm facing on some Acer/ Toshiba laptops and their BIOS/UEFI options v/s Multi Boot OS on partitions.
Originally Posted by Slartybart
I've tried initializing the drive as GPT, but the install converts it to MBR because my firmware is Legacy BIOS
You can only clean install Windows on a GPT disk if your firmware is UEFI (run msinfo32 to tell)
You can clean only install Windows on a UEFI system if the install media is a DVD or if the flash drive is formatted FAT32.
Deacon is right though, using dskpart clean before the install (Shift+F10 at the first install screen) makes sure that Windows does what it should do - create the proper disk schema for your machine
Windows 10 Forums is an independent web site and has not been authorized,
sponsored, or otherwise approved by Microsoft Corporation.
"Windows 10" and related materials are trademarks of Microsoft Corp.