Mac OS 9 Lives
Mac OS 9 Discussion => Mac OS 9, Hacks & Upgrades => Topic started by: smilesdavis on October 06, 2026, 10:05:27 PM
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Apple officially sold the G4 mini as having “no PCI slots,” yet internally it has a 33 MHz PCI host and Apple routed that PCI bus right to a removable expansion module.
https://leopard-adc.pepas.com/documentation/Hardware/Developer_Notes/Macintosh_CPUs-G4/MacMiniG4/2Architecture/q88_archi.html (https://leopard-adc.pepas.com/documentation/Hardware/Developer_Notes/Macintosh_CPUs-G4/MacMiniG4/2Architecture/q88_archi.html)
- the mini already contains a real conventional PCI bus
- The Intrepid I/O controller has a 32-bit PCI bus with a bus clock speed of 33 MHz.
- The connector for the AirPort Extreme Card uses the PCI bus.
- The mini's host bus is exactly the sort of bus your older Digi cards expect: 32-bit PCI at 33 MHz.
- Apple also used the same generation AirPort Extreme card across many G4/G5 Macs. Available Apple schematic material for that interface shows essentially the conventional PCI ingredients: AD address/data lines, C/BE, FRAME, IRDY, TRDY, DEVSEL, STOP, clock, reset, interrupt, REQ/GNT, IDSEL, etc. (https://www.informaticanapoli.it/download/SCHEMIELETTRICI/APPLE/Q45-G5-IMG5-051-6482-080304-RC.pdf (https://www.informaticanapoli.it/download/SCHEMIELETTRICI/APPLE/Q45-G5-IMG5-051-6482-080304-RC.pdf))
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Mac mini G4
│
AirPort PCI
│
custom PCBway interposer* for CardBus
│
Magma Chassis
│
┌─┼───────────────┐
PCI cards.....
a theoretical adapter should have its own regulated PCI power supply
Mac mini AirPort
PCI SIGNALS ──────────────────┐
GND ──────────────────────────┤
▼
PCI connector
▲
external PSU:
+3.3 V ────────────────────────┤
+5 V ──────────────────────────┤
+12 V ─────────────────────────┤
-12 V if required ─────────────┘
Grounds obviously have to be common.
G4 minis don't put the AirPort card directly onto the main logic board. They have a removable mezzanine board (820-1660-06) which can simply be removed from the motherboard, and replacement boards exist as Apple parts 922-6671 / 922-6893. The late 2005 1.33/1.5 GHz revision is less attractive, because Apple revised the mezzanine and integrated the wireless hardware more tightly. Earlier 1.25/1.42-era hardware gives us the nicest physical starting point.
That means I would not touch the Mac mini motherboard initially.
Mac mini motherboard
│
original mezzanine connector
│
donor mezzanine PCB
│
[remove AirPort connector /
attach interposer here]
│
normal PCI
┌────────────────────┐
│ Mac mini G4 │
│ │
│ Intrepid PCI │
│ │ │
│ AirPort connector │
└──────┼─────────────┘
│
│ custom PCB
▼
┌────────────────────┐
│ 32-bit PCI slot │
│ external power │
└──────┬─────────────┘
│
Magma
host card
│
║
║ Magma cable
║
┌──────▼─────────────┐
│ MAGMA 4-slot PCI │
│ │
│ MIX Core │
│ MIX Farm │
│ DSP Farm II │
└────────────────────┘