A Moogle  🏳️‍🌈 💻 🎮 🎶 🇸🇪

It was eventually determined that Sega had used an LCG for generating the sets of keys, which narrowed the search space a bit.

Beyond pure "copies simply won't run" protection, there were all manner of insidious methods in use. Sega's Quartet, for example, ran on System 16A hardware, but didn't have a Hitachi-encrypted CPU. It used a read-protected Intel i8751 microcontroller instead.

Among some fairly basic things - display enable/disable, for example - the i8751 MCU controls moving platforms in later stages. No MCU, no moving platforms. This is something only recently fixed in MAME, and which Sega even themselves got wrong in a recent re-release.

Moving along those lines, both Chack'n Pop and Bubble Bobble, from Taito, rely on a Motorola 68-series 8-bit microcontroller for protection. Certain critical aspects of gameplay are handled by it, including when bonus items appear, and enemy AI.

Patching out the initial protection checks to get the game to boot won't get you very far when the game logic itself is more or less hosed. This is a protection method Taito were very fond of, and would use in later games from the 80's as well.

Games like Operation Wolf, Rainbow Islands, and others used the "Taito C-Chip", which was a NEC uPD7811 and supporting circuitry, mounted on a substrate, and put in a DIP package to hide it. All of them rely on unique programs for various gameplay-critical elements.

Moving from gameplay to just sound, a wide variety of games from Toaplan such as Vimana, Ghox, Teki Paki, and others have all of the music playback and sound effects managed by a read-protected 647180 MCU. Same problem: No code, no sound.

One of the more horrid copy protection methods to break, done by Peter Wilhelmsen and the late Morten S. Kirkegaard, involved the Dallas DS5002FP secure MCU. As I understand it, it's primarily a combination of an Intel 8051 MCU, and a block of battery-backed encrypted RAM.