Multiple partitions with Windows 7 and OS X side-by-side install

When installing Windows and OS X side by side using Apple’s recommended Boot Camp technique, you can only use one partition for Windows.  If, like me, you need multiple partitions for Windows, you have to do it another way.  The first thing to understand is that Boot Camp Assistant is not at all necessary for installing Windows 7.

The other thing to understand are that the interaction between GPT/MBR (the new and old style partition tables) and EFI/BIOS (the new/old style firmware) makes things very tricky if you don’t understand the issues.

Several issues to know:

1) Windows 7 (and Vista too I believe) WILL install on a GPT partitioned drive and can also be booted from EFI firmware.

2) When the Windows 7 install DVD boots on a Macbook though, it actually boots in BIOS mode(!), this is because the Macbook will switch to BIOS mode when it sees that a DVD has a BIOS-based bootloader, which a Windows 7 install DVD of course will have.

3) When booted in BIOS mode, Windows 7 refuses to install on a GPT partitioned drive (this is what leads people to mistakenly think that Windows 7 does not support GPT installation)

4) However, and this is the kicker, even if you get the Macbook to boot Windows 7 (whether the installer DVD or the OS itself) in EFI mode, things will not work properly because the EFI version on Macbooks is the older version which Windows does not want to work with!  #$%@#$#@^@@….!!!!!  Windows 7, etc… *need* UEFI 2.0 to properly work with GPT partitions.

These 2 pages have more to say on the issue:

http://darobins.spaces.live.com/blog/cns!C188BEF79F825945!529.entry

http://www.insanelymac.com/forum/index.php?showtopic=186440

So how then do we install the 2 OSes side-by-side?  We’re left with two ways:

1) Hybrid GPT-MBR partitioned disk

or

2) MBR partitioned disk

From a Windows-centric viewpoint, method 2 is probably the cleanest and lets you deal with your partitions with standard tools like Partition Manager.  In this case, you will need to hack your OS X install DVD to install on an MBR disk.  The two links below explain how:

http://blog.netnerds.net/2009/10/easily-install-mac-os-x-leopard-on-an-mbr-formatted-disk/

http://www.insanelymac.com/forum/index.php?showtopic=181287

But because they involve extensive tweaking on the Mac command line which I don’t currently wish to involve myself in, I will go with method 1 instead which this blog article will explain further.

Firstly, a hybrid GPT-MBR disk is one looks like an MBR drive to older non-GPT supporting OSes but which GPT-supporting OSes sees as GPT.  As far as I understand, only the Disk Utility that comes with the OS X install DVD to create a hybrid GPT-MBR table correctly (if gParted can do this, drop me a comment…)

In my case, I needed 4 partitions, 3 for Windows and one for OS X.  In Disk Utility, I did the following steps:

1) Create 4 partitions in the partition editor, 3 as FAT and 1 as an OS X filesystem.  IMPORTANT: Make the OS X partition the last one.

2) (VERY IMPORTANT) Select GUID Partition table instead of MBR type using the Options button.

3) Apply changes and then reboot into the Windows 7 install DVD.

4) When the Windows 7 installer shows the available partitions you will see one extra 200MB partition at the beginning.  DO NOT DELETE THIS!  This is the GPT protective partition, deleting it will prevent Windows 7 from booting correctly afterwards.

5) The free space you allocated for OS X will show up as “unallocated free space”.  Do not panic.  This is because MBR only allows 4 primary partitions and they will already have been taken up by the GPT protective partition and the 3 primary FAT 32 partitions.  OS X uses GPT aand will see this last partition correctly, however, MBR cannot show it.

6) A side effect of pre-partitioning this way is that the 200MB (for Win7 RC) and 100MB (for Win7 RTM) “System Reserved Partition” will no longer get created.  Some people consider this an annoyance so this would be a good thing for them.

7) You can now proceed to format one or all 3 partitions via the Windows 7 installer.  This will turn them into NTFS, and allow install of Windows 7 on them.

8 ) NOTE: If you had installed OS X in Step 3, before booting into the Windows 7 Install DVD, the machine will default to booting in OS X, so you should hold down the Alt/Option key to see the Windows partition and boot from it instead.