Power Mac MDD Dual G4 1 GHz

Gentoo Linux

Bought in November/December 2008 via to help quench a thirst for PowerPC hardware ;) Later in December filled the remaining lonely RAM slot for a total of 1.5 GB (max 2 GB).

Linux drivers

ComponentKernel module(s)Notes
ATA/IDE drives (tried and true)ide-pmacProbe on-board ATA/100 (Kauai) first
ATA/IDE drives (new libata)macioCheck your yaboot configuration
Graphics / Xagp_uninorth, radeon
Graphics / consolefb_radeon
Sound / ALSAsnd_powermac
USBohci_hcd1.1 only
Firewireieee1394, ohci1394

Headless installation

I did not have an external monitor in my Kuopio residence, so I had to do a headless install of Gentoo. It was tricky at first, though I knew all the steps, since it took a surprisingly long time for the firmware to get to the CD drives. Another problem was that the kernel on the 2008.0 install disc was called ppc32, instead of 'apple' as mentioned in the handbook.

As usual for Macs, pressing the mouse button upon bootup will open the drive doors. Then pressing 'c' will boot from the CD. I had a DHCP server running on my laptop, so it was easy to see when the networking side had booted up. I then ran 'passwd' (giving the pw twice, as usual) and /etc/init.d/sshd start. Installation progressed remotely in the usual way.

Silencing modifications

The model is called Windtunnel in many references, including the Linux kernel menuconfig, for a reason. Many people have succeeded in denoising by simply replacing the power supply and CPU fans.

The CPU heatsink is indeed impressive and sensibly placed, compared to most x86 hardware. Apparently the main problem is with the PSU, as its air inlet is deep in the middle of the case, in a warm air bath. A little case modification could go a long way, possibly with ductwork via open/unused drive doors to preserve the vintage case.

[2009-02-09] I ordered quieter replacement fans for the power supply and the CPU, roughly following the above instructions. From Coolputer I found two pieces of Papst 612NGME and one Scythe Slip Stream 1200. While the Popes have nominally smaller flow rates, they have turned out a very good replacement for the PSU. After a week of continuous operation I have seen zero problems from this. The machine is quieter overall, but still far from tolerable in the living room.

However, the replacement CPU fan is notably inadequate, despite the rated flow equal to the succesful replacement in the above article. It may partially be due to the thinness of the Scythe that keeps it further from the heatsink, as well as its more disperse flow pattern. On the other hand, overvolting might do the trick, if I can find suitable voltages inside the Mac. For example, connecting the ground wire to -12 V while keeping the positive side at the regulator would give it a huge boost. Although, depending on how low the regulator can go, it could be way too much for the health of the 12-volt fan.

Solid state disks

[2010-02-23] These days, this machine has no need for huge storage, so it has become yet another testbed for my power-saving SSD experiments. It now boots off a Compactflash (via a passive PATA adapter), and the root filesystem is on a USB stick. A bigger CF alone could work as well, but I only had a 128-MB spare. That would probably be enough for a minimal Linux distro, but not so for a standalone Gentoo.

As a surprising result, the machine is much quieter and cooler without a hard drive. The HD noise had been nearly imperceptible behind the Windtunnel fans, but its placement next to the CPU heatsink apparently influenced the CPU temperature considerably. The airflow is not necessarily improved, though, as there is now an empty place, a bypass for air that could be used for CPU cooling. So this does open possibilities for further cooling mods ;)

Problems / TODO

Memory instability

[2009-09-04] There is a persistent instability following cold boots. Usually there are segfaults about 15 minutes after the boot, when the machine has warmed up to maximum temperature. A reboot usually solves the problem, and the machine can run stable for days. However, the reboot/halt stage itself is slow and unstable, and it often requires the Magic SysRq key.

Recently I have thought it may be due to the 400-MHz memory module that I have added into the 333-Mhz bus, otherwise populated by 333-MHz DIMMs. This sort of setup has generally worked for me, but Macs are known to be somewhat picky. Without that DIMM it seems to work fine so far.

The really interesting bit is the temperature behaviour. Perhaps the firmware identifies the memory capabilities differently at different temperatures.

Risto A. Paju