2015 21" iMac 4K [5th,2C,U] + RX Vega 56 Nano @ 16Gbps-TB2>TB3 (Gigabyte Gaming ...
 
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2015 21" iMac 4K [5th,2C,U] + RX Vega 56 Nano @ 16Gbps-TB2>TB3 (Gigabyte Gaming Box) + macOS 10.15.2 & Win10 1903 [itsage]  

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itsage
(@itsage)
Illustrious Member Admin
Joined: 4 years ago
 

This late 2015 iMac 21.5" came in to be wiped and recycled. There wasn't anything wrong with it so I made it into a Thunderbolt 2 eGPU testing system. It's as base as base can get but the performance is surprisingly decent.  😀 

 

System specs:

2015 21" iMac - i5-5250U/HD Graphics 6000 iGPU/8GB RAM/1TB HDD

 

eGPU hardware:

Gigabyte Gaming Box + RX Vega 56 Nano + Apple Thunderbolt 3/USB-C to Thunderbolt adapter & .5m Thunderbolt cable

 

Hardware pictures:

 

Installation steps:

Thanks to @Mac_editor's Purge-Wrangler script, the late 2015 iMac can use AMD eGPU in macOS Catalina. The RX Vega Nano Gaming Box worked through hot-plug and cold-plug as if it's natively supported. I tested external monitor output through an LG 4K and that worked well too.

It is a lot more work in Windows Boot Camp however. I was hoping with only the iGPU, it would be more straight-forward. Unfortunately error 12 was the culprit. Interestingly an Nvidia eGPU can work through hot-plug in Windows desktop (OS Build 18362.30). In order to solve error 12, I followed @nando4's instruction to do DSDT Override. Once I had the modified DSDT file, I used it with @goalque's automate-eGPU EFI boot manager to allocate Large Memory in Win10. Here are the step-by-step:

  • Install Windows 10 ISO through Bootcamp Assistant [in macOS]
  • Install DDU to remove all default graphics drivers and disable Windows automated driver installation [in Windows]
  • Create a 24MB FAT partition in Disk Utility and copy @goalque's automate-eGPU EFI onto it [in macOS]
  • Copy the 2015 21" iMac dsdt-modified.aml file to /EFI/CLOVER/ACPI/WINDOWS/dsdt.aml inside the EFI partition [in macOS]
  • Hold OPTION at boot to select EFI drive and hit Q to access automate-eGPU EFI [boot selection]
  • Install Intel iGPU drivers for the integrated graphics card then restart [in Windows]
  • Shut iMac down then connect eGPU to Thunderbolt port closest to Ethernet port [system OFF]
  • Boot into Windows via automate-eGPU EFI [boot selection]
  • Confirm a new Microsoft Basic Display Adapter in Device Manager then install Radeon drivers [in Windows]

 

Benchmarks:

In macOS I ran CL!ng and Luxmark 3.1 to check bandwidth and compute performance.

I ran Unigine and 3DMark synthetic benchmarks in Windows Boot Camp. First was internal display mode then next was external monitor mode through the LG 4K FreeSync monitor.

Internal Display External Monitor

 

Comments:

Apple Boot Camp drivers for the Intel iGPU were very old and produced bad performance. DDU not only helps removing them completely but also prevents Windows from installing older drivers by itself. Best performance is through an external monitor but the appeal of the iMac is to drive the internal display. An iGPU-only Mac allows AMD XConnect to accelerate the internal display automatically. Thunderbolt 2 reduced overall eGPU performance but it's significantly better than the iGPU.

external graphics card builds
best laptops for external GPU
eGPU enclosure buyer's guide

 
2013 Mac Pro (FP D500 x2) [3rd,12C,E] + RX 5700 XT @ 16Gbps-TB2>TB3 (Mantiz Saturn Pro) + macOS 11 [build link]  


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Enrico Franconi
(@enrico_franconi)
New Member
Joined: 2 months ago
 

Hi,

Thanks for your clear instructions! I'm not an expert, so maybe I'm asking a studpid question.

I have the same iMac.

Is the RX Vega 56 Nano a strict requirement for the eGPU, or would any eGPU work?

Which would be the optimal eGPU that would work with your instructions?

cheers

--e.

To do: Create my signature with system and expected eGPU configuration information to give context to my posts. I have no builds.

.

ReplyQuote
itsage
(@itsage)
Illustrious Member Admin
Joined: 4 years ago
 

@enrico_franconi, Most AMD cards released in the past 3 years should work with macOS. Given the Thunderbolt 2 connection and i5 U CPU, I would recommend RX 580 as the sweet spot.

 

external graphics card builds
best laptops for external GPU
eGPU enclosure buyer's guide

 
2013 Mac Pro (FP D500 x2) [3rd,12C,E] + RX 5700 XT @ 16Gbps-TB2>TB3 (Mantiz Saturn Pro) + macOS 11 [build link]  


ReplyQuote
Enrico Franconi
(@enrico_franconi)
New Member
Joined: 2 months ago
 

@itsage, would be the RX 590 also good?

And would be the RX 5700 XT an overkill? In other words, could I exploit its power with this iMac?

Thanks!!!

 

To do: Create my signature with system and expected eGPU configuration information to give context to my posts. I have no builds.

.

ReplyQuote