68kMLA Classic Interface

I enjoy tinkering with overclocking, and the G4 Mac minis are, in my opinion, the best Macs ever for this, unfortunately, they are hamstrung by limited RAM and GPU capabilities. In my humble opinion, the GPU is the real weak point there’s not much overclocking headroom, it’s limited to a 64-bit bus, and most models have only 32MB of VRAM. It’s frustrating to be able to squeeze 2GHz out of this little toy only to be held back by a "meh" GPU.

I’ve been brainstorming some wild ideas and discussing with a few contacts the possibility of creating an interposer to use an ATI Radeon 9600 or even a 9700 GPU. The first hurdle is the physical motherboard layout: there are two VRAM pads connected to the GPU via a 64-bit bus, and there’s no way around that. Then I remembered that there are versions of these chips with the VRAM soldered directly onto them that would make things much easier. The signals on the 9200 GPU pads are mostly the same as those on the 9600, though the physical ball layout, sizes, and so on might differ; that’s where a thin, carefully designed interposer would come in one engineered not to introduce impedance issues or mess up timing. Voltages and clock signals are controlled externally on the Mac mini motherboard, and they aren't vastly different. The main challenges would be figuring out the power delivery for the VRAM sitting atop the chip itself and potentially creating custom firmware by repurposing code from the PowerBook 17.

I’d love to hear your thoughts could this work as a community project, or did I just forget to take my schizophrenia meds today?

On my experimental G4 Mini, I've now successfully re-pasted the CPU and cranked it up to 1.58GHz, installed an SSD in a mSATA-to-PATA adapter, partitioned it 16 ways, and installed (and booted):
System 7.0
System 7.0.1*
System 7.1
System 7.1.2
System 7.5.0
Mac OS 7.5.3
Mac OS 7.5.5
Mac OS 7.6.1
Mac OS 8.0
Mac OS 8.1
Mac OS 8.6
Mac OS 9.2.2
OS X 10.2
OS X 10.4
OS X 10.5
OS X 10.6 PPC

On my experimental G4 Mini, I've now successfully re-pasted the CPU and cranked it up to 1.58GHz, installed an SSD in a mSATA-to-PATA adapter, partitioned it 16 ways, and installed (and booted):
System 7.0
System 7.0.1*
System 7.1
System 7.1.2
System 7.5.0
Mac OS 7.5.3
Mac OS 7.5.5
Mac OS 7.6.1
Mac OS 8.0
Mac OS 8.1
Mac OS 8.6
Mac OS 9.2.2
OS X 10.2
OS X 10.4
OS X 10.5
OS X 10.6 PPC

I'm still trying to get Mac OS 8.5.1 and Mac OS 9.0.4 to boot properly on it.

@indibil , I missed the trick to doing a 2GHz overclock. I can't imagine doing that without replacing the heat sink... I'm already blowing pretty hot at 1.58 and the original chip was binned at 1.42.

@ArmorAlley , I found that switching to mSATA SSD gave a significant speed increase, even over ATA-100. System 7.0.1 flies now! 😀

And I have to admit, under 10.6 I do notice the limitations of 32MB VRAM. There's a bit of distortion on my screen from time to time.

@Rikintosh , "carefully designed interposer would come in one engineered not to introduce impedance issues or mess up timing" is really the issue. I don't see how one would go about keeping the timing accurate enough without offloading a bunch to an expansion board directly from the bus, bypassing the clock-limited circuitry.

But if others have ideas, I'm more than willing to test them out. This is my salvage Mini that I've already thought I'd killed multiple times over, but it's still chugging along 🙂

Would enabling a 10/100/1GHz networking be possible or does the networking chip not support it?

I used FireWire networking between two Macs a few times and know next to nothing about it let alone how the FireWire 400 port bandwidth would be affected by any other hardware in a Mini, but could that offer an improvement? Not gigabit but a theoretical max of 50 MB/s vs 12.5 MB/s over the built-in Ethernet.