Classic Mac Hardware (Troubleshooting, Upgrading, & Modifying) > Mac OS 9 Booting on Previously Unsupported Hardware

Mac Os 9 booting on: xServe G4 (Detailed Posts)

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There is two models of DDR xServe G4:

A) A 133 Mhz System bus and ATA 100 Hard disk Interfaces and FW400.

B) A 166 Mhz System bus and ATA 133 Hard disk Interfaces and FW800.

In the A model the ATA 100 may help, but we are pushed to try the bus overclocking using the MDD procedure, never tested in the Xserve...

Getting rid the Open Firmware barrier to a  MacRISC2 kernel (Mac Os 9) it isn't easy, but it was done before. The real challenge comes now:

Comparing the PowerMac G4 MDD Architecture Block Diagram:

With the xServe G4 (133Mhz Bus) Architecture Block Diagram:

It's easy to see that the secondary PCI bus is really different from the MDD one. There is two PCI bridge interfaces ic (integrated circuit) and two ATA 100 ic. Probably Mac Os ROM 10.2.1 don't understand this part of the motherboard, so if don't bring it to a crash, it is better to ignore it by now.

So our possibilities must be limited to Uni-North 2 direct devices: Firewire, Ethernet, AGP etc...

This is the Simplified Block Diagram of the xServe G4 FW800 (slot load). The FW400 model is very similar but without FW800 ports :)

The light red zone is the more problematic one: the ATA ic and the PCI bridge. If Mac Os ROM 10.2.1 can't "drive" the first PCI bridge we lost the CD drive, USB and serial port etc. If Mac Os ROM 10.2.1 can't "drive" the second PCI bridge we lost The PCI slots! and the possibility of booting the machine with a Hard Disk connected to a PCI card! (SATA, FW, SCSI or USB)

In this picture, the blue color zones are the problematic ones, and the red are the VERY problematic ones...

So the procedure is:

- To use a basic installation of Mac Os 9.2 (ROM 10.2.1) in to a device connected to a port that this OS can "drive", We have to try FW, Ethernet, USB, PCI cards, etc...

- To trick the Open Firmware or Mac Os ROM to avoid the MacRisc3 closed door. For this we have to Hex Edit the ROM, change the NVRAM settings or in the last chance Reflash the firmware ¿?

Probably we have to remove some xServe components to try to avoid a system crash...

The successful possibilities are very low. In the best case we can achieve that the xServe boot in to Mac Os 9, but most of the components couldn't work...

In the worst case the xServe never go further than a grey screen, but at least, we try to learn something of the "inner soul" of this lovely machines...



--- Quote from: MacTron on October 30, 2014, 02:07:04 PM ---And try to trick the Open Firmware for Mac Os ROM to avoid the MacRisc3 closed door. For this we have to Hex Edit the ROM, change the NVRAM settings or in the last chance Reflash the firmware ¿?

--- End quote ---

in theory, you´d just remove the "risc3" entry (from somewhere at the beginning) of the rom. but maybe that also has disadvantes. :)

Here we have an intro to Macintosh boot:

The New World ROM also sets the "compatible" property of the root node to "MacRISC2" (machines that can boot classic Mac OS using "Mac OS ROM") or "MacRISC3" (machines that can only boot OS X or another Unix-like system).

So after the machine "basic" boot procedure (Open Firmware), we have to to enable a Mac Os 9 ROM to boot on a MacRisc3 Mac (the xServe, or any other Os X only G4). Here we have a guide on how to solve this:


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