BIOS Emulation - how to enable (mid 2010 iMac)?

Question

BIOS Emulation - how to enable (mid 2010 iMac)?

Two questions related to BIOS emulation:

I have a mid 2010 model iMac, does it support BIOS emulation? How can I find out?
Assuming I completely format my hard disk, how do I enable BIOS emulation, is it enough to have a hard disk with MBR partition table?

Rationale / Background:

I would like to dual boot Windows 8.1 and Ubuntu 14.04 on my iMac. I have no need for OSX (I have an external emergency USB HDD on which I have OSX 10.8 installed in case I ever need it).

Since I do not intend to use OSX on my iMac, it would not be recommended to use EFI to boot either Windows 8.1 and Ubuntu 14.04 because as far as I know, at least on the mid 2010 model iMac, Apple has implemented their own brew of EFI based on 1.x version and that apparently requires the "bless" feature in OSX for smooth operation and avoiding problems. So I would like to install and boot both Windows 8.1 and Ubuntu 14.04 in BIOS emulation mode.

Posted on Aug 4, 2015 7:24 AM

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Answer 1

Loner T

Level 9

59,471 points

Aug 4, 2015 8:30 AM in response to PartisanEntity

The HDD is not really impacted by BIOS, but by the disk partitioning and formatting. All Intel Macs support a BIOS emulation layer called CSM-BIOS, but it has no user interface.

Ubuntu will work on EFI that Macs use which is 1.1. UEFI is not supported on your Mac, so Windows will need CSM-BIOS and a Hybrid MBR on top of the GPT disk partition scheme.

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Answer 2

Aug 5, 2015 8:08 AM in response to Loner T

So if I set up my hard disk with Hybrid MBR, is that all I need to do to get Windows 8.1 to install in BIOS- emulation on my iMac?

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Answer 3

Loner T

Level 9

59,471 points

Aug 5, 2015 8:59 AM in response to PartisanEntity

If you want to, post the output of the following Terminal commands.

sudo gpt -vv -r show /dev/disk0

sudo fdisk /dev/disk0

The "sudo" commands will prompt for your password, and it will not be echoed back. You may also see a warning about improper use of "sudo" and potential data loss due to "abuse" of the command.

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Answer 4

Aug 5, 2015 1:03 PM in response to Loner T

I use Ubuntu as my main OS on the iMac, so here is the output of

sudo gdisk -l /dev/sda

instead:

GPT fdisk (gdisk) version 0.8.8

Partition table scan:

MBR: protective

BSD: not present

APM: not present

GPT: present

Found valid GPT with protective MBR; using GPT.

Disk /dev/sda: 1953525168 sectors, 931.5 GiB

Logical sector size: 512 bytes

Disk identifier (GUID): 21090AD7-A749-4E86-84E8-68BA38EDF40A

Partition table holds up to 128 entries

First usable sector is 34, last usable sector is 1953525134

Partitions will be aligned on 2048-sector boundaries

Total free space is 821044589 sectors (391.5 GiB)

Number Start (sector) End (sector) Size Code Name

1 2048 1050623 512.0 MiB EF00

6 822091776 1928376319 527.5 GiB 8300

7 1928376320 1953523711 12.0 GiB 8200

The HDD is currently in Hybrid MBR as you can see. Based on what I have been reading, I can convert the disk into full-on regular MBR.

I guess I will wipe the disk using an Ubuntu Live USB, convert to full-on regular MBR and then install Windows 8.1 ?

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Answer 5

Loner T

Level 9

59,471 points

Aug 5, 2015 3:18 PM in response to PartisanEntity

The disk has a Protective MBR, not a Hybrid MBR. Can you post the output of

sudo gdisk /dev/disk0

x

o

q

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