DualBoot Info 4 Old and New Mac's

Contributor II

Hi everyone,

Since I spend heaps of time scripting and organizing our dual boot OS deployments. I thought I would share a little info since Apple's documentation and the way they want you to do things is very rubbish.

Things that one MUST take into consideration if your deploying OS X via Casper, and deploying Windows via SCCM.

Remember! New Mac's post late 2015 can only boot from EFI/UEFI external devices.

Windows 8 and newer... Can boot Windows setup via UEFI and be installed on an GPT partition! ie a partition flagged as GUID/GPT

Why? god why? Is apple still through funky wizardry and manipulation of BootCamp assistant forcing Windows to be installed on hybrid MBR?

diskutil will by default, create a hybrid MBR for any partition within the first 2TB thats FAT32 or exFAT on disk0.

In order to prevent diskutil from creating a hybrid MBR partition, you must use the JHFS+ file system type.

This will leave the partition as a GPT partition type. Then during a Windows installation if you delete it and create an NTFS partition in its place, Windows can use it to install Windows to.
We have a script in Casper used by Casper Imaging that lays down our dual boot partitioning layout. Then OS X and Windows can be built and rebuilt independently of each other.

Starting a windows installation via UEFI booting will automatically create the MSR required partition (hidden). SCCM won't, this needs to be performed prior to starting your SCCM OS build task sequence.

We make SCCM USB boot media that's UEFI capable which can boot new Mac's. We use them to start our SCCM OS build task sequence. We've scripted converting our partition number we know is the Windows volume to be a hybrid MBR for old mac's and UEFI for new mac's. SCCM then builds our Windows environment like any other Dell, Lenovo, HP, or whatever PC running Windows...

While diskutil (OS X) can use drive usage percentages (%) in scripts, diskpart in Windows can't and can only use fixed MB sizes.

Windows can actually be scripted to apply correct MB sizes, but it requires too much scripting in calculator functions etc... I'm too lazy!

Windows can't be installed or deployed to to any partition that either overlaps or is beyond the 2TB limit, Mac or PC.

Anyways. hopefully this helps someone, somewhere.