In advance, sorry for the wall of text. I wrote this up in a text editor (too large and important for the web interface). Also too large to fit into a single post. I divided it in about half and posted each portion separately.
One day I was obsessing over how technology might cross over from our civilized world into a world of an apocalypse.
One of our most important inventions is the computer. It allows us to store massive amounts of data, communicate over long distances, and calculate very quickly.
Without advanced (not to mention computer assisted) fabrication labs, there's no chance of fabricating a modern CPU. There's also no real way to reverse engineer them, as they're way to small and complex to analyze.
There is a CPU that's not as complex: MyCPU! http://www.mycpu.eu/ There is an advantage to this in a post apocalyptic world. It's possible to build one entirely from discrete components. Possibly components salvaged from broken electronics that we find strewn all over the world. There is, however, disadvantages. Chiefly of which, is it is very large. We cannot be sure how we will live in a post apocalyptic world. If the Fallout series is any indication, many of us will be nomads, constantly in danger. At a moment's notice we might have to grab what we can and flee. MyCPU, in addition to a monitor and all, will not be taken with you.
We need something portable. Somthing that can fit in your hand. Something that's durable and can possibly be replaced.
I stumbled upon this: http://www.youtube.com/watch?v=EBeTXPaewMo As you can see, gameboys are made from a material known as Nintendium (lol) and are indestructible.
It also has other advantages. For a computer to be useful, you need a way to communicate with it and it a way to communicate with you. Also, a way to communicate with other computers (the Gameboy link cable). The Gameboy integrates a screen and user input. However, the most useful input device is a keyboard. A PS2 keyboard can be hacked with an appropriate connector to interface with the gameboy.
According to wikipedia, there have been 200 million units produced in the Game Boy Line (including GBA, etc.): http://en.wikipedia.org/wiki/Game_Boy_line
It's also low power. In fact, it can be hacked to charge via solar power: http://hackaday.com/2011/04/04/solar-powered-gameboy-color-never-runs-out-of-juice/
To be useful in the future, a computer must be reprogrammable. Preferably self-hosting (even more important in postapocalyptia). A simple flash cart will not do.
The arduino is a very flexible platform. It offers endless nights of hackery. Unfortunately, video is not trivial for an arduino. I also don't fancy carrying around a CRT with me in post apocalyptia, unless it's integrated into an armband like the Pip-Boy.
The advantage of a cartridge is that you can put whatever performance enhancing thing you want into them. You can even stick another processor in them. This has been done in many old game consoles that use cartriges. Like how yoshi's island has the SuperFX processor to do sprite transformations. Unfortunately, we cannot fit an arduino into a gameboy cartridge. Luckily, we can fit an AVR processor in there. Well, some of them. Just for kicks, I opened up an old gameboy game I didn't care too much about (I wouldn't touch my pokemon like I did this), removed the PCB, and put the ATMega from my arduino into the cartridge. Unfortunately, the DIP package is too tall, so we need to use a surface mount version.
Also, in post-apocalyptia, hacking will be even more important than it is today. I envision a row of female headers on the top of the cartrige like on each side of an arduino.
It's also essential that it has a mass storage device. SD(HC) cards can solve this problem quite handily. I think there should be at least two slots for SD cards in the cartridge. It would be preferable if one could be an external port. I say at least two SD card slots so you can have your programs on one and deal with removable storage. At least one should be full size SD if possible, because miniSD and MicroSD have their adapters. There should also be a FAT32 driver so we won't be limited to 2GB (alot of data in the world is stored on SDHC cards). I think data recovery would be an essential function of rebuilding the world. So much literature, art, history, and science is stored on computers.
It should have a way to interface with a keyboard. I think the most common way would be to use a PS2 keyboard. You could cut off the connector and plug the wires into the top ports or you could rip a PS2 socket out of an old motherboard, solder wires to it, and plug those into the top port. Then you can plug in your keyboard or any other PS2 device. I'm sure a number of legacy connectors could be used in this way.
Today, there are billions of USB device. That's not a made up statistic: http://en.wikipedia.org/wiki/Usb "As of 2008, approximately 6 billion USB devices had been sold in total, and about 2 billion were being sold each year." I'd kill myself if I didn't at least try to put a USB host on this board. Anyways, a little research turns up this: http://www.circuitsathome.com/products-page/arduino-shields/usb-host-shield-2-0-for-arduino/ There's also a smaller version: http://www.circuitsathome.com/products-page/arduino-shields/usb-host-shield-for-arduino-pro-mini/ Integrating the circutry into the PCB containing the ATMega further shrinks the size down. As I said before, there are billions of USB devices. Plenty of them store massive amounts of data, including flashdrives and even USB harddrives. The harddrives are particularly advantageous because they don't have limited write cycles. However, a standard USB plug is too big to fit on top, especially if we want the top to be filled with female pins like on the arduino. One method would be to wire two of those pins as USB data port. Two of the pins already need to go to 5V and GND and can be reused. You could pick up any old USB hub and cut off the male end and have it plug into your cartridge. It might also be possible to mount a USB port on the front of the cartridge where it says "Nintendo GAME BOY TM" and has that indention. This also allows the possibility of USB keyboard and mouse, bluetooth or wifi dongles, etc. in addition to your flashdrives (maybe at the same time, but our ATMega wouldn't have much bandwidth for each item). One especially exciting notion is that there are IDE and/or SATA to USB devices. I have an IDE to USB device (for netbooks). Using this you can access desktop harddrives and use IDE CD/DVD/BluRay drives. This would be especially useful for recovering movies and music from the past. Seriously, look at ANY suburban home. You'll find a rack, a closet, or some other place that's PACKED with the stuff.
Continuing the subject of post-apocalyptic data recovery, and more specifically art, why? Well, obviously, I don't think any of us care to carry Justin Bieber with us into the next era (post-apocalyptic or not), but art is an integral part of culture. There's also documentaries that explain how technology works, about specific times and places in history, and other useful things. The art also captures the mood of the day.