Re: grub-efi with latest mac mini

[Chris Murphy]

On Jun 8, 2012, at 12:50 PM, Vladimir 'φ-coder/phcoder' Serbinenko wrote:

> On 08.06.2012 20:34, Chris Murphy wrote:
> 
>> a.) Mac Mini's EFI implementation can use either MBR or GPT schemes for 
>> booting.
>> 
>> b.) If this is a dual boot situation, Mac OS X is EFI only, effectively 
>> requires GPT and an EFI System partition. Your particular Linux distribution 
>> support of Apple's unique EFI, which is not UEFI, determines whether you 
>> will boot Linux or Windows or whatever you're booting, either in EFI mode, 
>> or CSM (BIOS emulation) mode.
>> 
> 
> Wrong. EFI doesn't require GPT or other round.

I never said it did.

> Mac OS X installer will
> refuse to install on GPT but if you force it, Mac OS X will be able to
> boot alright.

As I said, in effect, Mac OS X is EFI only and requires GPT. The number of 
people who will either hack the installer, or convert from GPT to MBR or APM is 
perhaps in the dozens,  or <0.1% of Apple hardware owners.


> Also Mac OS doesn't use EFI system partition other than
> for firmware updates.

Unclear. All Apple computers with Mac OS X running, have an identical 
Firmware.scap file installed to the EFI System partition. The file is placed 
there after system installation, but before software updates, and without user 
permission - unlike firmware updates. I don't know what it is used for.

In any event, present usage of this partition type isn't an indicator of future 
usage. At any time Apple could start using it, e.g. with Boot Camp to support 
Windows 8 EFI booting.

> You mix again 2 things: you can boot in BIOS mode (CSM) on pure GPT as
> well. Windows is an exception since Microsoft pretends that possible is
> impossible.

False. Apple's CSM will not activate unless the following three things are true:

1. MBR is present, with more than one entry.
2. At least one MBR entry must have the active flag set.
3. The first 440 bytes of the MBR can't be zeros. i.e. there needs to be 
something that looks like a boot loader might be present.

If any one of those three things is not true, the CSM will not activate on any 
of the 1/2 dozen hardware models I've tested this on. It appears to be by 
design.


Chris Murphy