Sonic the Hedgehog CD (Mega-CD prototype; 1992-12-04)/Technical information

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Sonic CD, as with all Mega-CD games, uses a filesystem with files for each code event instead of a monolithic rom. Splash screens, menus, and levels all reside in their own MMD file with optional BIN files for SubCPU execution.

As each MMD runs separately of others (except for those which load to RAM), various pieces of code and data are repeated throughout like MMD files. This makes art editing without a disassembly very long and tedious. However, upon the release of a disassembly of Sonic CD 0.02, all common art and code will be consolidated so changes are reflected in every MMD including that data.

The level MMDs have the filename format RXYZ__.MMD:

• X is the zone. R1 is zone 1.
• Y is the act. R12 is zone 1, act 2.
• Z is the time period. There are 4 letters that can be put here; A, B, C, or D. A is the present period. B is the past period. C is the bad future period. D is the good future period. So R12D__.MMD would contain act 2 of zone 1, in the good future period.