Post #3744043
2026-07-11 12:05 UTC
I think I just found a 40 year old Easter egg.
I was looking into the Levco Monster Mac, which is an upgrade board for the original Macintosh 128k/512k which adds up to 2mb of ram as well as SCSI.
An interesting feature is that this upgrade doesn't necessarily require Macintosh plus ROMs to work (most expansion cards do, as the original ROMs only work with 512k of ram, and don't have SCSI support).
Fortunately the ROMs for the Levco Monster Mac have been dumped.
https://archive.org/details/levco-monstermac-2mxs-rev-d-proms_202505
I reassembled the ROM from the high and low ROM dumps, looked at the resulting binary with a hex editor and there's a nice little greeting for people poking around the ROM 😂
Replies (1)
-
@me_@sueden.social 2026-07-11 12:38
@DosFox@tech.lgbt Nice, I never saw one of these! It seems the EPROMs on the board are located at 0xf80000 in the address space and identify themselves as a test ROM (0xaa55 at offset 2), so the ROM code (starting at 0xf800a8) is called early during system startup from this piece of code in the Mac 128/512k ROM: https://github.com/jonathanschilling/mac_rom/blob/1d1014e1f85b0e2fab42ffcffbddf3770b9fbefc/original/boot/vectors.s#L83