One of the coolest things to come along in the 68K Mac homebrew community is the ROM Boot Disk concept. Classic Macs have an unusually large ROM that contains a fair bit of the Mac OS, which was true even in the G3 New World Mac era (it was just on disk), so it’s somewhat surprising that only one Mac officially could boot the Mac OS entirely from ROM, namely the Macintosh Classic (hold down Cmd-Option-X-O to boot from a hidden HFS volume with System 6.0.3). For many Macs that can take a ROM SIMM, you can embed a ROM volume in the Mac ROM that can even be mirrored to a RAM disk. You can even buy them pre-populated. How’s that for immutability?Well, it turns out Apple themselves were the first ones to implement a flashable Mac OS ROM volume in 1994, but hardly anyone noticed — because it was only ever used publicly in a minority subset of one of the most unusual of the Macintosh-derived systems, the Apple Interactive Television Box (a/k/a AITB or the Apple Set Top Box/STB). And that’s what we’re going to dig into — and reprogram! — today.
I had never heard of this obscure Apple product, so I was like a kid in a candy store reading this. Great weekend material.