Gyruss C64 prototype

1984 Parker Brothers

Platform: Commodore 64

Not quite a GTW64 entry, but an earlier build of the released Gyruss (a brilliant Konami arcade conversion) for the C64 – recovered thanks to preservationist Ken Van Mersbergen.

This prototype dated 2nd May 1984 was found within the collection of disks/materials from the archive of a retired programmer who used to work for Roklan and On-Time Software.

There doesn’t seem to be much in the way of differences that we’ve found so far apart from slightly different attack waves.

Professor Chaos got in touch via the comments to say that there are two differences to the final version and described by him as “theoretical or VERY rare glitches”. One in particular was where it goes straight to a level complete animation when all the enemies finish exploding.

In the final version, an extra check is added to make sure you are still alive (as you could still run into an enemy shot for example). Another difference was the removal of some code that when an enemy’s sprite block is blank, it’s y-position is set off-screen. Professor Chaos suggests that maybe this was unnecessary and removed to make room for the above fix in the first difference.

So, not a major difference to the final version at all – but good to see these different builds preserved, as you just never know what may surface.

A huge thank you to Ken Van Mersbergen for his fantastic preservation work and for preserving this prototype. Thank you to Professor Chaos for checking through the code and highlighting the minor differences present.

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4 Responses to Gyruss C64 prototype

  1. From comparing both versions using a machine code monitor, I can tell that there are two differences, no more. Though they seem to be only theoretical or VERY rare glitches. I couldn’t find ACTUAL differences while playing either.

    In case other gamers or coders want to watch and dig deeper:

    First off, after all enemies finished exploding, a routine at $8A15 gets called. In the prototype, $8A15 goes straight to the level-completed-animation. In the final version, this was added:
    ,8A15 LDA $3100
    ,8A18 BEQ $8A2E
    So it first additionally checks if you’re alive. (Remember, after shooting the last enemy, you can still run into its shot.)

    From the final version, this was removed instead:
    ,8A38 LDA #$70
    ,8A3A STA $2759,X
    If an enemy’s sprite block is blank, its y-position is set off-screen. Maybe this was unnecessary and removed to make room for above fix.

    The other few byte differences are merely code relocation.

    • Thanks Professor Chaos for going through the code! Does indeed look like this was practically the released version then, and any changes were very minor tweaks.

    • I suspect it is pretty much the final release. Though I had something odd happen when I played and the levels seemed to complete quicker, and I had infinite lives up to around Level 10 (before it went back to normal). Not sure if there was some kind of Easy feature in the original and final release?

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