This prototype is a bit of a mystery.  The EPROM covers don't have anything written on them, so we have no idea what date or version it is.  In fact the only identify mark is a long label on the back that says Vanguard.  This prototype tests out differently than the released version, but the differences in the code are very minor and not visible in the game itself.

 According to Thomas Jentzsch (who was kind enough to analyze the code for me), the final version of the game had two "emergency exits" that would skip some code if the previous code block took too long.  This was done to prevent the game from occasionally using extra scan lines which might cause some colors to disappear.  These "emergency exits" are missing from this prototype, which is what causes the checksum to test differently.  However this happens very rarely so I've never been able to witness it in this prototype.


The Tunnel of Love this isn't!


Stix Zone (I'm sailing away...)



These guys look like Space Invaders rejects


Talk about safe sex...



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