Disabled iGPU in some Mac models
Not directly eGPU related, but relevant. I have a late 2014 27" iMac (the 4Ghz i7 version), with "no integrated graphics". Just a discrete AMD GPU.
Only it does have an iGPU - an intel HD 4600! Intel's spec sheet for the CPU says it has one, and running AGDCDiagnose lists it. But it's not present in System Profiler and it's not (easily) accessible to developers.
Anyone know what the deal is? Is the iGPU present but physically disconnected somehow? Or is it just disabled in firmware? And can it be re-enabled? Even if it's not useable for drawing, it's useable for compute - and while it's only 1/10th the speed of the dGPU (never mind the eGPU the fact that it shares system memory can make it faster for certain specific tasks.