64 GB of RAM DOES indeed work in a Mac Pro 2,1, check it out.

Base fan speeds are set to whirl at a constant 1500RPM, keeping the DIMMS at or below 80C. Should the need arise, they can be set to 1700. Beyond this, however, the fans are loud.

I generally post in Facebook computer user groups, as Apple Support communities generally are oriented toward user-end problems, instead of allowing upgrades such as the ones I have performed.

Upgrading to a Mac Pro 2,1 from a 1,1 requires 2 total steps:

1: Replace your CPUs with Dual Xeon x5365 processors.
2: Download the Mac Pro 1,1 2,1 firmware upgrade utility tool. After rebooting and applying the firmware, this may result in detecting only one processor. Reboot, and you should be fine.

If you're looking to upgrade to 64GB of RAM on a Mac Pro 1,1 or 2,1, make sure of the following:

1: You're running OS X 10.8.0+, as it's exclusive to 64-Bit Kernels, which would allow your Mac Pro to register over 32GB of RAM, despite having a hacked/borked 32-bit EFI boot loader.

2: If you're willing to face the project head on, please do so: 32/64GB of RAM would produce plenty more heat than your standard 16GB/below config, so if you're buying non-Apple RAM modules, replace the heatsinks with Apple heatsinks. I did this, and my temps dropped from the 70-80C range, down to the 40-50's.

If you have further questions, contact me at:

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I have undertaken the work required to replace the ill-working thin, wafer-like server heatsinks on the 8 GB FBDIMMS, over to official Apple heatsinks. Temps are now (on avg) 35-45C cooler.

There are several upgrade paths available for your Mac Pro, still. System-software wise, I strongly recommend Mac OS X Yosemite 10.10.5 with a modded boot.EFI file, as it is a very stable system for the Mac Pro 2,1. El Capitan works and is stable, however, I cannot give you accurate information, since the decision to not use El Cap on my own machine has been influenced by the fact I own and operate a GTX 960 in my Mac Pro 2,1, and the Nvidia Web Drivers are quite spotty with the releases that do and don't work. Given that a working release must remain with a particular OS version, I stick with 10.10.5. I spent nearly half a year on 10.10.0 using the only known version of the Nvidia Web Drivers which worked for my PNY GTX 960, before they released a properly working graphics driver version for 10.10.5. Take this with a grain of salt, for I see you're not looking to purchase a newer PC-based video card.

For you to use more than 32GB of RAM on your Mac Pro 2,1, you must be running a 64-Bit Kernel. If you are running any OS up to 10.7.5, the included 32-bit EFI would force you to boot into a 32-Bit Kernel (I think that's how it is), therefore, rendering anything above 32GB totally and utterly useless. Then again, my explanation may be marred, for the sake that I used Leopard on a G5 for 7 years, and jumped right to OS X Yosemite on an older Mac Pro. Either way, I know that a 32-Bit Kernel limitation would result in a 32GB ram limit. Using any OS after 10.7.5 would force you to boot into a 64-Bit Kernel, even if using a modded 32-bit EFI, since the older EFI was dropped starting on OS X Mountain Lion, hence, why 2007 Mac Pros cannot "officially" support 10.8+.

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