At glance, the unit looks almost identical to the Nintendo 64DD that hit Japan in 1999 -- so much so that when Jason "MetalJesusRocks" Lindsey found it, he assumed it was merely a US developer kit. Turns out, it's even more rare: the unit boots up without the aid of the "partner cartridge," developers needed to get devkits running. It also features an english-language menu screen, something not present in official development units or the original Japanese retail model. The unit is even region-locked to the US, and won't play japanese N64DD games. Lindsey (and Ars Technica) reached out to Mark DeLoura, a former Lead Engineer at Nintendo that worked on the n64DD, to figure out what was going on. The answer? This is most likely an unreleased retail unit, or at least a retail prototype.

That alone makes it a rare collectors item, but there's one more mystery surrounding this retail prototype: it came with a unreadable, blue game disk. The development cartridge is unlabeled, and Lindsey has been unable to get it to boot so far -- but DeLoura says the disk could contain a US retail-ready N64DD game or some of the demos he used to show the device to developers when he still worked for Nintendo. Lindsey says he's working with the gaming community to find a way to read the disk. With any luck, we'll have one more piece of Nintendo history to admire sometime in the near future. Until then? Check out Lindsey's YouTube channel for a full rundown of the rare, retail hardware.