What is EFI partition?
The EFI system partition (ESP) is a small partition formatted with FAT32, ususally 100MB, where stores the EFI boot loaders for the installed system and applications used by the firmware at startup. If your hard drive was initialized as GUID Partition table (GPT) partition style, it will generate an EFI system partition after installing Windows or Mac operating system (OS).
Normally, you cannot view it in File Explorer because it have no drive letter. If you delete this partition accidently, it will cause the installed system unbootable. Therefore, in order to protect this partition, Windows will not allow you to delete it easily. Nevertheless, there are situations that people want to get rid of the EFI partition.
How to delete it?
As mentioned before, the EFI partition is essential for the installed OS on the hard disk. However, for an external hard drive, you do not actually need the EFI partition. Some users had the EFI partition created on a Mac, and now they want to install Windows to replace Mac OS. In this case, they need to delete the EFI partition and generate a new EFI partition for Windows. To delete this EFI partition, you can use third party partition manager software AOMEI Partition Assistant Pro that can delete any partition without losing data on other partitions.
To delete EFI partition with AOMEI Partition Assistant:
1. Install and run this program.
2. Connect a USB drive or CD to your computer and click “Make Bootable Media” and follow the wizard to create a bootable disk.
3. In the main interface, right click on the EFI partition that need to get rid of and select “Delete Partition”.
4. In the pop out window, click “OK” to confirm.
5. You can see EFI partition has become an unallocated space, and you can add this unallocated space to any of the existing partition by using Merge Partitions function. For now, the program has made no changes to your hard drive, and you can click “Apply” button to apply the operations if it is as you required.
Besides deleting EFI partition, AOMEI Partition Assistant can do many other things that Disk management cannot. It can convert disks between GPT and MBR without data loss, create bootable media, move partition, and many more.
How to create EFI partition?
For booting Windows on a GPT disk, there must be an EFI system partition and a Microsoft Reserved Partition (MSR) on the disk. If someone delete the EFI partition on the system disk by mistake, the Windows will fail to boot. In this case, you need to create an EFI partition and then install EFI boot loader to make the hard drive bootable. Besides, migrating or installing OS to another hard drive alongside the original system disk, the new hard drive might fail to generate an EFI partition. Once you remove the old hard drive, the system will not boot. If you happened to lose an EFI partition on your system disk, you can follow the steps below to create one.
1. Boot your computer from a Windows installation disc or recovery disk. Press Shift+F10 in the setup to enter command prompt window.
2. Run the commands below to shrink a partition to get unallocated space.
Select disk X (X represents the disk number of the disk that needs an EFI partition)
Select partition N (N represents the partition number of the partition that needs shrinking)
Shrink desired=500 (shrink the partition by 500MB)
3. Then you can create EFI partition out of the 500MB unallocated space using the command below:
create partition EFI size=200
format quick fs=fat32 label="System"
create partition msr size = 128
4. After those two partition have been successfully created, use the commands below to install boot loader and other applications needed.
bcdboot c:\Windows /s b: /f ALL
to fix boot record.
5. Reboot your computer to see if it is fixed.
If your computer fails to boot because of missing the EFI system partition, you can use this method to recreate it, and then you can get your Windows system back as before. Even though this will not cause data loss, it is also recommended to create a disk backup before you make any changes.