EFI is for Extensible Firmware Interface
The EFI System partition (ESP) is a partition on a data storage device that is used by computers adhering to the Unified Extensible Firmware Interface (UEFI). When a computer is powered up and booted, UEFI firmware loads files stored on the ESP to start installed operating systems and various utilities. (Wikipedia)
EFI is more like a layer to protect against badware by requiring a digital signature from the bootloader. EFI is currently replacing already old MBR (Master Boot Record). EFI uses more modern GUID Partition Table (GPT) so from now on your computer will see hard disk larger that 2TB.
Windows users noticed that sometimes their computer using Windows 8 and EFI fails to boot, bootloader seems to be damaged and Windows cannot boot.
In this case it would be great if you have a Windows 8 USB recovery drive, if you don’t have it, you will need Windows 8 on a USB drive, or on a DVD.
Fix EFI Bootloader
Start up your computer from the USB Driver or DVD Windows 8 recovery media in the system. After you will have to go to the “Advanced options“.
When the computer boots from the recovery media, from the menu choose “Troubleshoot”
From the next menu choose “Advanced Options”
and the last choose “Command Prompt” from the menu
Now the computer should reboot and ask you to Login with your password. After that we will see a dark screen with the command prompt. In the command prompt type down the following commands.
Type the following command to see all our disks:
and enter this command:
sel disk 0
We selected the first disk, let’s list all partitions we have:
Verify that the EFI partition is using the FAT32 file system and select it to assign a drive letter to it,
Note! I am using VirtualBox image, and in the screenshot above you won’t see the FAT32 parition, but on your computer you will see it. Select it by noting the volume number.
Step 1. Assign the Drive Letter
For example if your EFI partition is on Volume 3, you will have to type following:
sel vol 3
Now we have to assign a drive letter to the parition. Let’s use F.
Now you will see a message that says:
DiskPart successfully assigned the drive letter or mount point.
Exit the diskpart tool by typing exit, do not exit from command prompt, we have to go to the next step.
Step 2. Repair the Boot Record
To repair the boot record, write following commands, and don’t forget the drive letter we assigned R.
Using cd command we will change the directory:
cd /d r:\EFI\Microsoft\Boot\ With bootrec command we will repair the selected volume:
3. Rebuild the Boot Configuration Data
After all these commands we will have to recreate the Boot Configuration Data (BCD) store. But before we will have to backup the existing store.
To backup type the following command, this command will rename the BCD, so it won’t be automatically replaced:
ren BCD BCD.old
Now let’s recreate the new BCD store:
bcdboot c:\Windows /l en-us /s r: /f ALL
BCDBoot is little tool that lets us to manage the system partition files, and the last command is to update all the BIOS settings.
If you are sure that you did everything right, reboot your computer, but before remove remove the recovery media.
More Useful Things
Did you know that Windows 8 has mouse lag issues ? Check your Windows 8 for mouse lag issues:
Also if you are a Linux user, you should know How to Repair GRUB after Intalling Windows.