Default EFI partition configuration

Question

Level 1

8 points

Default EFI partition configuration

Hello,

I need to know what the default EFI partition should look like.

I installed Windows 8 via EFI and then removed it and it left its bootloader behind which keeps defaulting to the primary startup disk, so I deleted the Microsoft portion and now it wont boot all by itself, just a gray screen leading to nothing. Holding down Option will allow me to select the correct disk but I'd like to get this working again.

So here are my questions:

1. What does the default EFI partition look like? File structure I mean.

Here are the commands in case you need them:

#mkdir /Volumes/efi
#diskutil list

/dev/disk0
   #:                       TYPE                   NAME                                 SIZE       IDENTIFIER
   0:      GUID_partition_scheme                                             *251.0 GB     disk0
   1:                        EFI                                                            209.7 MB   disk0s1
   2:                  Apple_HFS                Macbook HD                 151.0 GB   disk0s2
   3:                 Apple_Boot                Recovery HD                  650.0 MB   disk0s3
   4:                  Apple_HFS                Bootcamp VM                  99.0 GB    disk0s4

#sudo mount -t msdos /dev/disk0s1 /Volumes/efi
#ls /Volumes/efi

2. Does the Windows install edit the /Volumes/efi/Boot/bootx64.efi file?

If you need any new info to help me out please let me know.

MacBook Pro with Retina display, OS X Mountain Lion (10.8.4)

Posted on Jul 17, 2013 1:26 PM

Reply

Answer 1

mende1

Level 10

93,624 points

Jul 17, 2013 1:30 PM in response to whoopn

That's the reason why Apple doesn't support Windows installations via EFI. I tried it in my iMac and Windows also modified the EFI partition. Some bootups later, Windows started showing BSODs, and when it was working, I was lucky if Windows could start up.

The EFI partition is hidden and is used to store firmware updates in order to be installed during the startup. Now, Windows has used it to store the Windows boot files, so you may have problems installing firmware updates. The structure looks fine, but the problem is that it's not being used for its original purpose.

Respecting to your second question, bootx64.efi is the Windows startup file, so of course that Windows copies that file to the EFI partition and is edited as needed.

My advice is to reinstall OS X starting in Internet Recovery (holding Command, Option and R keys while your Mac is starting), erase the whole storage with Disk Utility, install OS X and then, install Windows again. And never install Windows in EFI mode if you aren't completely sure about what you are doing

Reply