I have a 2009 Mac Pro, which has been upgraded to a MacPro5,1. It's currently running macOS Sierra. I was going to upgrade it High Sierra, but the High Sierra installer said it needs to first update the firmware and asked me to proceed in doing that.

I'm nervous to allow this to happen since the firmware was already upgraded from a MacPro4,1 to a MacPro5,1.

Also, I'm running a flash NVIDIA GTX 980, which has the boot support. I'm afraid this might cause problems as well.

Are there any known issues or conflicts with my configuration or similar configuration when upgrading to High Sierra?

  • Related - apple.stackexchange.com/questions/299769/…
    – Tetsujin
    Commented Dec 31, 2017 at 7:29
  • "I'm nervous to allow this to happen since the firmware was already upgraded from a MacPro4,1 to a MacPro5,1." This doesn't make sense. MacPro4,1 and MacPro5,1 are hardware designations -- they refer to physically different computers.
    – user101978
    Commented Dec 31, 2017 at 7:44
  • 1
    @duskwuff - more research required. This has long been possible. The 4,1 & 5,1 are so close physically that you can fool the system into thinking one is the other & then uprate the hardware accordingly, Nehalem to Westmere CPUs. Picture showing a 4,1 with 5,1 firmware & higher than original spec hardware upgrade - i.sstatic.net/dtleW.png These machines can also update beyond El Capitan, once tweaked.
    – Tetsujin
    Commented Dec 31, 2017 at 8:32
  • Tetsujin is right. It's fairly easy to upgrade a 4,1 to 5,1 and install Westmere processors. I have a 4,1 upgraded to 5,1 dual processor 2.26 upgraded to 2 x 3.33 GHz X5680 and a 4,1 single quad processor 2.66 GHz upgraded to a a 5,1 six core 3.46 GHz X5690. No problems for me adding High Sierra firmware update to the dual processor and still being able to boot Sierra and El Capitan. Have not tried older OS since the firmware upgrade. Commented Jun 7, 2018 at 20:17

2 Answers 2


I was able to perform the firmware upgrade with no problems. The MacPro upgraded the firmware after I held the power button until it flashed, then prompted me to install High Sierra after. It rebooted a few times in-between.

  • I only had a single boot after holding the power button until it started flashing. The long bong came about a minute later. Commented Jun 7, 2018 at 20:30

The firmware update deals with new file system (APFS) I also have a 2009 4.1 flashed to 5.1 - the firmware update went ok!

...but during the start up, or when restarting i get prohibition sign, just for for a second or two - then it goes away and system boots to mac OS HS 10.13 no problem, just longer. After googling i found a sugestion to re-install OS through option +R

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