Assuming it is disk 0, type these commands which will remove all partitions from the HDD and make it into a totally empty unformatted drive. SELECT DISK 0. CLEAN. Now reboot from the USB and try the install again. Select the Custom Install option and you should now be able to install in the unallocated space. exit. Then the drive will appear as a single unallocated space on the custom install drive and partitions list. As addional clarification, occasionally, it is sometimes necessary to upgrade bios to see all of space even on a GPT drive - some older pcs limited maximum size to e.g. 3GB. It`s a brand new drive, no partitions. The only thing you may have to do is initialize it (the new drive) if it asks. And it should ask. When you get to the page that shows the drive is all unallocated space, all you should have to do is click next. Make sure the unallocated space is highlighted. Attached Thumbnails. When you remove Disk 0, what is shown as Disk 1 in the image will be disk 0 on next boot. Delete the Partition 1 from it so then it will only show one instance of Drive 0 Unallocated space. Select that as the drive to install to, and windows will partition it as needed and install windows. After it's complete, reconnect your second physical drive. Partition 1 - Recovery. Partition 2 - System - The EFI System partition that contains the NTLDR, HAL, Boot.txt, and other files that are needed to boot the system, such as drivers. Partition 3 - MSR - The Microsoft Reserved (MSR) partition that reserves space on each disk drive for subsequent use by operating system software. Highlight the unallocated space and click next. What @ dalchina alluded to. On the screen where there is a list of drives and partitions, highlight each partition and click delete until you have disk 0 showing as nothing but unallocated space. Highlight the unallocated space and click next. .

what is drive 0 unallocated space