create a bootable usb for powerpc mac g3

CREATE A BOOTABLE USB FOR POWERPC MAC G3 MAC OS
CREATE A BOOTABLE USB FOR POWERPC MAC G3 UPDATE

It’s just an Open Firmware Forth script that contains the new ROM data to flash to the chip.

CREATE A BOOTABLE USB FOR POWERPC MAC G3 UPDATE

I could desolder the chip, reprogram it, and solder it back on, but why bother if there’s a way to do it directly from software? So I grabbed Apple’s G3 Firmware Update 1.1 and inspected it. The firmware update just re-flashes the chip with new data. Apple created firmware updates for several of the New World Macs. These machines are different, though–the “boot ROM” (as I have been calling it) is actually a flash chip that can be programmed in-system. My past customization experiments have required hardware modifications to change the chime. OK–so at this point, I knew it could be done. I would venture a guess that it’s stored in that exact same format in all New World Macs. I’ve looked at the ROM from all of my other New World Macs, and the sound is stored in the exact same format in all of their ROMs as well.

The uncompressed sound is a 44.1 kHz, 16-bit mono sound that is just under 2.5 seconds long–so anything that is 2.5 seconds or shorter should work fine as a replacement. After some detective work combined with lucky guesses, I figured out that the sound is a chunk of 58,548 bytes compressed using Apple’s version (IMA 4:1) of the IMA ADPCM compression format. I played around with the ROM from my G3 Blue and White by opening a dump of it as raw sound data in Audacity and found the sound, but I could tell it was compressed. I have several New World Macs, and they all have the exact same startup chime. I discovered that the startup chime on these Macs is also stored in the 1 MB boot ROM.

CREATE A BOOTABLE USB FOR POWERPC MAC G3 MAC OS

Open Firmware is capable of loading a file from the hard drive (typically called Mac OS ROM) which contains the rest of the ROM that older machines had on a mask ROM chip on the logic board. The boot ROM also provides Open Firmware which gives them a lot of flexibility for doing things before the operating system has loaded. They have a 1 MB boot ROM on the logic board which does the initial setup of the machine. They call them “New World” because they use a totally different style of ROM from previous Macs. These computers are powered by the PowerPC G3, G4, and G5, starting with the original iMac.

I’ve moved on to the next stage of my Mac ROM startup chime hacking, toward the late 90s to mid 2000s machines - the New World PowerPC machines. My post today is about another startup sound hack I’ve just completed. Maybe I’ll create a post about that later. I have yet to talk about it on this blog, but I have also created a USB programmer for the ROM SIMMs. Then, later, I actually had a programmable ROM SIMM PCB manufactured that works with many Macs from the late 1980s and early 1990s. As you may recall from the past, I’ve taken a Mac IIci and hacked a new startup sound into it.

Create a bootable usb for powerpc mac g3