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...