Seth Michael Larson: Extracting Genesis & Game Gear ROMs from SEGA GameCube collections

The GameCube library had multiple SEGA game collections: Sonic Mega Collection, Sonic Adventure DX, and Sonic Gems Collection which all contain ROM files for the Genesis and Game Gear (among others).

We'll extract the ROMs from each collection and then compare these GameCube collections to modern SEGA game collections like Sonic Origins Plus and the Genesis collection for Nintendo Switch Online.

TLDR: If you're picking one of above collections to buy for ROMs, the Sonic Mega Collection is my recommendation. 10 Genesis games with ROMs for $10 is an incredible deal, and it includes three of the best games in the Genesis library being Sonic the Hedgehog 2, Sonic 3 & Knuckles, and Ristar.

Sonic Origins Plus is pretty good deal for the games in the collection. If you're deciding between Origins and Sonic Adventure DX you're basically picking between Sonic 1, 2, 3 and CD versus the main story of Sonic Adventure DX. I'd probably pick Sonic Origins Plus over Sonic Adventure DX. If you do buy Sonic Origins Plus for ROMs, make sure you buy from Steam.

Sonic Gems Collection is a strange one. Two-thirds of the value comes from two games: Sonic R and Tails' Skypatrol, which might be up your alley, but if not then this collection isn't for you. The Sonic CD, Sonic R, and Sonic the Fighters files included aren't actual ROMs, instead they are DOL files so need to be played on a GameCube emulator.

Genesis for Nintendo Switch Online isn't worth it right now especially as a yearly subscription. The collection is sorely missing Sonic the Hedgehog 3 and Sonic & Knuckles. Over time this collection might be actually worth the money, but in all honesty it's tough to beat the value of the Sonic Mega Collection.

Buying any of these collections is an affordable and quality starting point of a ROM collection for an emulator. Here's a breakdown of which games are in which collection and their prices:

NOTE (1): The soundtrack for Sonic the Hedgehog 3 (and thus, Sonic 3 & Knuckles) has been changed since the original release. I prefer the original soundtrack, so if you do too then know that it's not included with "Sonic Origins Plus".

NOTE (2): Japanese editions of Sonic Mega Collection also contain both Vectorman and Vectorman 2.

NOTE (3): Japanese editions of Sonic Gems Collection also contain Bonanza Bros and Streets of Rage 1, 2, and 3.

Sonic Mega Collection

Sonic Mega Collection contains the ROMs for 10 Genesis games that are all compressed using SEGA "PRS" compression. Unfortunately there's no magic string for PRS compression, you just have to know that's what is being used:

• Dump and open the ISO in Dolphin.
• Right-click the ISO, Properties, Filesystem tab.
• Under sonic/data/ select the roms directory. Right-click and select Extract.
• Download and compile this C++ program. ($ g++ dat2bin.cpp -o dat2bin)
• Run the program on all .dat files ($ for f in *.dat; do ./dat2bin $f ${f::-4}.md; done)
• Truncate the ROM knu_p2u.md to 3407872 bytes ($ truncate knu_p2u.md --size=3407872). For whatever reason, this ROM decompresses with a few NUL bytes at the end.

Not only does Sonic Mega Collection contain ROMs from actual cartridges, the collection also includes the "ROMs"knu_p1u.md, knu_p2u.md, and knu_p3u.md which are the result from combining Sonic & Knuckles with Sonic the Hedgehog 1, 2 and 3 using "LOCK-ON Technology".

After decompressing the ROMs you should end up with files with these checksums:

Sonic Adventure DX

Sonic Adventure DX contains the ROMs for 12 Game Gear games. Extracting them is similar to Sonic Mega Collection, but the PRS compression has changed slightly so you need a different decompression script.

• Dump and open the ISO in Dolphin.
• Right-click the ISO, Properties, Filesystem tab.
• Unfortunately there aren't any directories to help us here. I recommend extracting the whole disk into a directory.
• Download this Python script and Python 3.11+.
• Run $ python prs-to-gg.py *.prs and the Game Gear ROMs will be decompressed.

Sonic Gems Collection

Unfortunately the ROMs in the Sonic Gems Collection aren't simply compressed, they are obfuscated using a custom routine. The most interesting titles that distinguish Sonic Gems Collection from others (Sonic CD and Sonic R) aren't stored as ROMs for their respective systems. Instead, these games appear to be compiled as DOL files, meaning they can't be played using a typical Sega CD or Sega Saturn emulator.

• Dump an open the ISO in Dolphin.
• Right-click the ISO, Properties, Filesystem tab.
• Under ggrom and mdrom_us select all the .cpt files.
• These .cpt files are the obfuscated ROM files.

There appear to be many more ROMs than are playable within the game itself, maybe hinting that this collection is more worth it than at first glance?

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