Sonic CulT // Sonic - Prototypes // Sonic The Hedgehog 2 // Findings

Leftovers in the ROM
Leftover data from previous builds
Inside the Sonic 2 prototype ROM is a series of lost data that tells about earlier builds. When programming a Sega Genesis/Megadrive game, they used various PCB boards, which allowed the programmers to attach chips.



Whenever a new revision was made, it was burnt onto the chips over the old data on the chips. When doing so, the data was written onto the chip a bit randly, leaving open spots on the chip that it didn't write over. Basicly meaning that whatever data was in these "holes" can still be explored. The following information is a collection of descriptions of some of that leftover data. (Special thanks goes out to Nemesis for allowing me to copy his detailed guide word for word.)


End of compressed ARZ 128x128 block mappings
This small reminant of a rather recent build indicates a minor change in the above blocks of data, which resulted in a slightly shorter file size. This was most likely just a minor amendment to the block mappings for a level, resulting in them not compressing quite as well.

large chunk of CNZ 128x128 block mappings
This contains a large proportion of an earlier version of the CNZ 128x128 bl This contains a large proportion of an earlier version of the CNZ 128x128 block mappings. The block of data is missing the first 3340 (D0C) bytes. From this we can see a massive chanage in CNZ between this compilation and the one in our beta. These block mappings have been changed so radically, that only a pattern in thier layout is recogniseable when compared to our current beta one. This indicates a massive restructuring in the order of the 16x16 block mappings of this build as well, but unfortunately that data was written over.

CPZ patterns/block mappings
These are the complete patterns and block mappings for an earlier version of CPZ. There are a few minor changes in the patterns, and some fairly major changes in the 16x16 and 128x128 block mappings.


leftover data

the active data


Compressed ARZ 128x128 block mappings
This lost data is in an uncompiled form, and at first I mistook it for code. Apart from the fact it is in this form, the data appears to be very close to that of our current beta. There is a commented line at the very start of the block, which contains further information about the block of compressed data. Thanks go out to Iceknight, who figured out that the text in this comment was in Kanji, and thanks go out to Kojichao and sth2k for translating it. The commented line reads:
Before compression $8000 After compression $2c00 Compression ratio 34.4% Cell number 1024
I had already guessed the purpose of the first three numbers, But I still can't figure out the puropse of the last one, or at least not one that would be worth putting in a comment. If anyone has any idea what the fourth number is used for, let me know.

Half of SEGA intro sound
This is a large proportion of the sega intro sound from an earlier compilation. There do seem to be minor differences in the waveform, but for the most part it's identical to the one in our beta and the final version.

Pattern load cue's
Due to changes in the structure of the rom, there are quite a few pattern load cue's left from previous compilations. In fact, in this one small area in the rom, I have identified six different layers of lost data from previous compilations, and these compilations seem to be a lot newer than the remains of level data judging by some of the link locations on the cue. Here's a breakdown of the lost pattern load cue's:

24804End of boss level (unknown boss/unknown boss/small explosion/smoke trail/EHZ boss/unknown)(?)[5]
24828ARZ (lever spring/V spring/H spring)(?)[1/2+1]
24838Title card (title card patterns)(0)
24840End of signpost level (signpost/hidden bonuses/unknown)(0)[2]
24854End of boss level (unknown boss/EHZ boss/unknown/unknown boss/unknown boss/small explosion/smoke trail/EHZ boss/unknown/)(2)[8]
2488CEnd of boss level (smoke trail/EHZ boss/unknown)(?)[1/2+1]
2489CMCZ (log/invalid pointer (7976C)/V spring/H spring)(?)[3]
248B4CNZ (invalid pointer (AB748)/invalid pointer (AE75A))(1)
248C2CNZ (spikes/D spring/V spring/H spring)(3)
248DCCPZ (invalid pointer (B1D24)/stuff/striped blocks/unknown/big platform/small platform/spring stopper/water/unknown/stuff)(9)
2491ACPZ (spikes/unknown/invalid pointer (7976C)/V spring/H spring)(4)
2493AARZ (invalid pointer (B9686)/water/leaves/arrow shooter/splash)(4)
2495AARZ (spikes/invalid pointer (7976C)/V spring/H spring)(3)
24974Title card (invalid pointer (7E222))(0)
2497CEnd of signpost level (signpost/invalid pointer (7F37A)/invalid pointer (7F206))(2)
24990End of boss level (invalid pointer (7C4BC)/invalid pointer (7D942)/invalid pointer (7E12E)/invalid pointer (7C4BC)/invalid pointer (7CBF8)/invalid pointer (7D7DE)/invalid pointer (7D85C)/invalid pointer (7D942)/invalid pointer (7E12E))(2)[8]
249C8ARZ (invalid pointer (?AD00)/invalid pointer (7976C)/V spring/H spring)(?)[1/2+2]
249DCTitle card (invalid pointer (7E222))(0)
249E4End of signpost level (signpost/invalid pointer (7F37A)/invalid pointer (7F206))(2)
249F8End of boss level (invalid pointer (7C4BC)/invalid pointer (7D924)/invalid pointer (7E12E)/invalid pointer (7C4BC)/invalid pointer (7CBF8)/invalid pointer (7D7DE)/invalid pointer (7D85C)/invalid pointer (7D942)/invalid pointer (7E12E))(2)[8]

Back To Game Index
Back To Sonic The Hedgehog 2 Index