Believe it or not the 2009 Mac Pro which outperforms some of the latest Mac models has been blacklisted from having macOS 10.13 High Sierra installed on it. Why? Who knows...But, with a little nerd skills you can get your 2009 Mac Pro updated to the latest version of macOS (which at the time of writing is 10.13 High Sierra).
I previously had gotten 10.12 installed which required a little hackery but was well worth it to get my system running on the latest version of macOS. High Sierra requires a firmware update so that your 2009 model is seen as a 2010 model. Thankfully this is relatively easy to do if you have some spare time on your hands and a little patience. Here's what you're going to need:
- 2009 Mac Pro 4,1
- A USB stick which is at least 8GB in size
- A copy of OS X Mavericks
- An extra hard drive (I had a space 500GB SATA laying around I used)
- The firmware patching tool
- The EFI Updater from Apple
I initially had some trouble running the firmware patching tool on my Sierra installation so this I did some further digging and some other folks found that going from Mavericks would work fine. The error I was getting was 'Error 5570'. I utilized the following guide to make a bootable USB of macOS Mavericks. I had previously purchased a copy of Mavericks from the App Store so I just downloaded it using that method.
So once, you've gotten your bootable USB setup, get Mavericks installed into your spare hard drive. Then you'll want to grab the firmware patching tool, and the EFI updater from Apple. I am not positive why this was necessary, but I had to open/mount the EFI updater from Apple, then run the firmware patching tool. It's possible this post here explains why, but I am not sure if that's it. Anyways, get the EFI Updater mounted, then run the firmware patching tool. The only button on the firmware patcher that should be clickable is the 'Upgrade to 2010 Firmware'. Click that and the tool will do its thing. If all went well you should get a little informational popup telling you to shut your Mac Pro down. Follow through on that information. If that works out, you'll hear a long tone while starting up your system and the firmware will be updated!
You can open the System Profiler application and on the page it opens to, you'll see the firmware information. The Boot ROM Version should read 'MP51.007F.B03'. Great! Now shut down the system and put your original hard drive back in. Snag the free macOS 10.13 High Sierra installer from the App Store and run it. It may tell you an additional firmware update is needed. Follow through on that. Once booted back into macOS, you can visit the System Profiler and your Boot ROM Version should read, 'MP51.0084.B00'. The High Sierra installer application should also be already opened. Go ahead and install!
Once all is said and done and you're booted back to your desktop, you should have the latest firmware for the system and you'll be running at least macOS 10.13.2 High Sierra. I have yet to test out updates to the OS via the App Store, but if they've been anything like previous unsupported installs they'll work perfectly fine! Good luck!