I know that it is possible to tri-boot a Macbook Pro with OS X, Windows, and Linux, giving each OS one partition. However (and I know I am probably a little crazy for suggesting this), is it possible to quad-boot one with OS X, Windows, and two kinds of Linux? (The two kinds of Linux in question would probably be Arch and either Ubuntu or Fedora.) From what I have read, it seems like the hybrid MBR/GPT combination required for multi-booting means that you are limited to a maximum of four partitions, one of which is used by the Macbook as an "EFI system partition," and this scheme would require at least five (probably six or seven, if I wanted a swap partition and/or shared storage). Has anyone attempted this before?
I have lots of multiboot machines. Yes, you can quad boot. Be aware that any LEGACY OS that needs bios will have to be in the first 4 partitions. Since EFI takes up the first one, and MacOS is usually next, you only have two options for other windows. The linux should work fine at any location.
I originally had Lion on my new iMac. Wanted my old Snow Leopard because of incompatible apps. So, after trial and error and finding this magic '<4' partition number... I reformatted my entire system to Snow Leopard, BootCamp'd to get Windows. Then use Disk Utility to shrink the Mac partition to whatever size you want and make additional partitions between the Mac and Windows. These are 'new' partitions, so they get added at the end, meaning they are 5, 6, etc. Not physically, but logically. I then loaded Lion and Mountain Lion on them... Install rEFIt on the booting partition (first mac partition, marked primary), and the refit menu allows you to boot each OS.
As far as I understand (I've never owned any Apple hardware, though), recent Macbooks run EFI and natively boot from a disk with a GPT. A hybrid MBR is then installed to dual boot Windows, which has inadequate support for GPTs.
Linux supports GPTs well, and though it is commonly booted from the hybrid MBR on Macbooks, there is no reason it could not be booted natively from the GPT. As far as I can tell, this is described for Ubuntu in this wiki, it is likely accomplished somewhat differently for other distros.
The three-OS limit (or whatever) could only stem from the limited number of partitions possible in a hybrid MBR (two or three, depending on whether you use one or two protective partitions), where at least one is required for each OS booted from the MBR and possibly one for a bootloader or something (OSs booted from the EFI should not need an entry in the MBR iirc. I don't claim intimate knowlege of Macos, though).
However, (Linux) OSs booted from EFI would not be part in the limitations of the MBR. You should be able to create very many GPT partitions and boot a different OS from each as easily as you can install a single OS that way.
You could boot any number of Linuxen with only two partitions, one boot partition with kernels and initramfsen and one with an LVM.
Anything above will at the very least require a lot of fiddling with Macos's bootloader (assuming it has one) and a generic bootloader (probably GRUB or eLILO).
I built a fresh, stock mountain lion mbpR, created recovery disk on usb with apples recovery disk assistant tool. Boot to the usb recovery tool, use disk utility to ADD windows 8 partition, Linux mint 14 "/" mount point partition, Ubuntu "/" mount point partition, and swap partition. All additional partitions were created as FAT by disk utility, to be reformatted by the operating system using them during installation. load installation media and begin installing OS's to their respective partitions. I use rEFInd as my efi booter.
i have run into stumbling blocks getting this set up cleanly, but it is pretty simple once you go through it twice. Missing operating system messages are the most common, but are trivial fixes. i have read some method on natively achieving a quad boot as well. I'll be trying those as well.