I was recently poking around inside the original Power Macintosh G3’s ROM and accidentally discovered an easter egg that nobody has documented until now.
This story starts with me on a lazy Sunday using Hex Fiend in conjunction with Eric Harmon’s Mac ROM template (ROM Fiend) to look through the resources stored in the Power Mac G3’s ROM. This ROM was used in the beige desktop, minitower, and all-in-one G3 models from 1997 through 1999.
As I write this post in mid-2025, I’m having a really difficult time accepting the fact that the Power Mac G3 is now over 27 years old. Wow!
While I was browsing through the ROM, two things caught my eye:
First, there was a resource of type HPOE which contained a JPEG image of a bunch of people, presumably people who worked on these Mac models.
This wasn’t anything new; Pierre Dandumont wrote about it back in 2014. However, in his post, he mentioned that he hadn’t figured out how to display this particular hidden image on the actual machine. Several older Macs have secret keypress combinations to show similar pictures, but the mechanism for displaying this one was a complete mystery.
I recently found myself needing to change the monitor that a cheap HDMI “dummy plug” pretended to be. It was a random one I had bought on Amazon several years ago that acted as a 4K monitor, and I needed it to be something simpler that didn’t support a 4K resolution. The story behind why is a long one that I’m still figuring out and might eventually become a separate blog post in the future.
If you’re not familiar with dummy plugs, here’s a quick primer: they are tiny dongles you can plug into an HDMI, DVI, etc. port that don’t actually do anything with the video signal. They simply have the minimum circuitry needed for a video source device, like a computer, to think that a monitor is hooked up. In general this entails a pull-up resistor on pin 19 (HPD) to +5V, as well as a little I2C EEPROM chip containing the Extended Display Identification Data (EDID). This is useful for headless machines to force the OS to think a monitor is attached.
The EDID contains all the info about the monitor: the manufacturer, manufacture date, supported resolutions, audio channels, color space, and stuff like that. My goal was to replace the dummy plug’s EDID with an identical copy of an EDID from one of my many 1080p HDMI capture devices. Then, the computer I plugged it into would think the capture device was plugged in instead of a 4K monitor, and everything would be hunky dory.
