Hi, about a month ago my Atari 600XL got delivered, and one of the things that came with it was this odd looking thing. From what I can gather, it might be for the Vic-20, as it fits in my C64's modem slot. I've seen RAM expansions for the Vic-20, but all the ones I've seen go in the cartridge slot. I can't seem to find any info about this thing on the web, so any insight would be nice.