This info has likely been discussed before but I can't find it via searching. I'm trying to understand the USB 3.0 architecture on the late 2015 27' iMac, specifically, how many controllers/busses are behind the 4 USB ports and how much available bandwidth there is. I am considering a new computer for my music composition pursuits and between TB-based outboard DSP for my effects (UAD TB Satellite), external SSD storage for sample libraries and external storage for DAW projects/stem recording, I'm concerned about getting everything connected without tanking storage throughput (which impacts sample streaming, which in turn impacts number of voices).
I know the TB2 ports share a single controller on a 4 lane PCIe 2.0 connection, so those are limited to roughly 2 GB/s. If the USB ports are split across 2 full bandwidth buses, I can probably make this work. Otherwise I'm looking at a nMP. I was going to go used there, but I'm now slightly concerned about the GPU problems and reliability.
I know the TB2 ports share a single controller on a 4 lane PCIe 2.0 connection, so those are limited to roughly 2 GB/s. If the USB ports are split across 2 full bandwidth buses, I can probably make this work. Otherwise I'm looking at a nMP. I was going to go used there, but I'm now slightly concerned about the GPU problems and reliability.