Screenshot(s) of the day: Ultima IV, Redux

At last, the screenshot I spent several hours of retrogaming working toward.

What you see above is my favorite bug in all of videogames, in the Commodore 64 version of Richard Garriott's RPG masterpiece Ultima IV: Quest of the Avatar. When I was a child, I and my brothers nicknamed it "The Twilight Zone." It is shown to best advantage when your party of adventurers is in possession of a hot-air balloon, and it took me some time to acquire that balloon.

The bug is possible because, from time to time as you wander the surface world of Britannia, the C64 must access the disk drive. Unlike the transitions to and from towns and dungeons, these brief loads occur without prompt or warning. The program doesn't check to see whether the right disk is in the drive when it does these loads, and it doesn't throw an error if the wrong disk is in there. What you see above is what happens when you put Disk 4 -- the "Underworld" or dungeon disk -- in your drive. (This can be done in emulation as well as on an actual Commodore 64, by simply attaching the wrong disk image at the appropriate time.) After the routine short load, the normal landscape of Britannia begins to fall away, replaced by a quasi-random assortment of dungeon tiles, monsters, lava, letters, and the like. Most of these tiles aren't functional -- they are frozen and act as walls -- but the floors can still be traversed, and sometimes there's grass that you can land your balloon on. (You could also venture into the "Twilight Zone" on foot, but given the extremely uneven dispersal of terrain types, you're unlikely to be able to get very far.)

Once you've landed your balloon in what seems like a hospitable spot, you may be lucky enough to stumble upon one of the few functional tile-types in the "Twilight Zone" -- treasure chests! And so I was able to do yesterday:

Best of all, these aren't normal treasure chests that you can open just once. You can open them infinitely many times, until you've maxed out your party's gold-carrying capacity at 9999. As long as you have enough heal and cure spells to ride out the inevitable traps, you can just keep looting away:

Once you've filled your pockets to your satisfaction, it's simply a matter of walking back to where you parked your balloon, taking flight, and inserting the Britannia disk (or its virtual counterpart) back into your drive. Then you await the next disk access, and voila! the comforting old landscape begins to scroll back into view:

All is as it was, except you're a few thousand gold pieces richer. This is what makes it my favorite bug in videogames. It's weird, surprising, completely reversible, and extremely practical. Whether it can be replicated on any other computer system is something I don't know, but I wouldn't be surprised to see it on an Apple II, assuming the breakdown of data distribution across floppy disks was similar.

Comments

[Tristan Miller]

This was my favourite exploit as well—though it never occurred to me to use the balloon, and I didn't release that the chests were infinite. As I recall, the trick also worked in Ultima V, which was a godsend when trying to get past tricky bits of the Underworld. (Just flip the disk to the Britannia side, walk around the obstacle, and then stick the Underworld side back in!)

I wonder what happens in Ultima IV or V when you flip the disk before entering a dungeon room. Ever tried?

[Gordon Cameron]

Hi Tristan, thanks for your comment! I never did try doing the reverse flip, until just now. The result will be my next screenshot of the day. :) Unfortunately it wasn't very playable.