OS X Mountain Lion can run on unsupported Intel Mac Pros
While unsupported, if needed, Apple's earliest Mac Pros can be used to run Mountain Lion.
A new procedure has surfaced that may allow owners of the older and unsupported Mac Pro 1,1 and 2,1 machines to run Mountain Lion natively on their systems.
When Apple initially released OS X Mountain Lion developer previews to testers and its development community, word spread that the OS would leave out some of Apple's earlier Intel-based Macs, including the first Mac Pro systems that still pack a decent amount of computing power. Apple made these requirements official more recently on its OS X up-to-date Web page for Mountain Lion.
The reason for these limitations revolved around two aspects of the new OS. First, Mountain Lion has new graphics requirements that cannot be performed with the older Geforce 7300GT and Radeon X1900XT GPUs that shipped with the first Mac Pros. Additionally, the OS no longer includes a 32-bit version of the OS X kernel, meaning it will not load on systems that have either 32-bit chips or 32-bit EFI firmware. Unfortunately, despite their inclusion of fully 64-bit capable CPUs, the first Mac Pros use 32-bit EFI firmware.
These developments were disappointing for early adopters of Apple's Intel Macs, especially when the Mac Pro with its multiple 64-bit Xeon processors, ample RAM capabilities, and options for graphics card upgrades ought to run the new OS just fine. For these models, the only detail preventing Mountain Lion from running is a compatibility with the systems' firmware. While some have argued that Apple could potentially make its 64-bit kernel run on systems with 32-bit firmware, Apple has not done so and likely will not take any steps to implement this or provide firmware upgrades for the unsupported Mac Pro systems.
While these details have prevented Apple from officially supporting these systems, for those who own them there is a ray of light that may allow them to run Mountain Lion, if they so choose. A new procedure outlined at Jabbawok's blog (derived from a procedure outlined at netkas.org originally for using the 64-bit kernel on older Mac Pro systems) shows that these systems can be used to run Mountain Lion by first upgrading their graphics cards and then using an emulated 64-bit EFI firmware that is commonly used to load and manage multiple operating systems on PC hardware.
Upgrading the graphics card is fairly simple and can be done using the Apple-supplied and supported Radeon HD 5770 kit that is available from the Apple Store. Unfortunately the simplicity of this process ends there; it requires you use a secondary internal drive as an intermediary for modifying the OS X boot loader and copying specific system files in order to allow the Mountain Lion installer and OS to run.
In addition to the complexity of the procedure, it is not guaranteed to work, and since the final setup will not be a supported configuration by Apple, it may result in a less stable system. Because of this, the Jabbawok procedure should more appropriately be recommended as a hobby for curious users rather than a concrete solution for those needing to install Mountain Lion on their early Mac Pros.
A final note is that this procedure will only work on the Mac Pro systems. Other unsupported Macs like iMacs, Mac Minis, and MacBook systems have graphics cards that cannot be upgraded; therefore even if the emulated firmware is installed, on these systems Mountain Lion will likely hang or crash when loading or performing certain tasks.
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