On legacy BIOS systems that use the MBR partitioning scheme, the BIOS checks partitions marked as active for startup files necessary to boot the system.
Most modern systems use UEFI with GPT partitioning style in which the UEFI keeps a list of boot entries corresponding to files in the EFI system partition. As such, the concept of active partitions is deprecated in UEFI systems.
This is why, if you attempt to mark a GPT disk as active, you’ll encounter the self-explanatory error message:
“The selected disk is not a fixed MBR disk. The ACTIVE command can only be used on fixed MBR disks.”
One thing that’s worth mentioning is that UEFI systems do contain a protective MBR, but the active partition in this MBR is ignored. The UEFI instead uses the EFI Boot Loader to boot from the EFI system partition.
It should be evident now that this isn’t an error as much as it is intentional design. However, this can still be a roadblock in certain cases. For instance, you may need to mark a partition as active to create a bootable USB or something similar.
In such cases, you can work around this error by converting the GPT disk to MBR. The disk will be cleaned during the conversion, so you’ll want to back up the contents elsewhere first.
You must also make sure you select the correct disk to clean and make active. Cleaning the wrong disk will wipe everything from it. Additionally, on MBR systems, marking a partition without boot files as active can cause booting issues. With that said, here are the necessary steps:
- Press Win + R, type
diskpart, and press Enter. - Enter
list diskand note the disk # of the disk you’re trying to convert.
- Type
sel disk 0, replace 0 with the disk # if different, and press Enter. - Execute the following commands:
clean
convert mbr
- As the clean command clears all partitions, use the
create partition primarycommand to create a primary partition, then use theactivecommand to mark it as an active partition.
