Turtles all the way down: SoCs and Storage

This brings us along to designs that are rather common even though we don't normally think of them as either common or systems. By this, I refer to SoC's - Systems On A Chip. As the name implies, they are full (or nearly so) computers implemented as single mother-huge silicon chips (relatively speaking). On the die you'll find a CPU or microcontroller, supporting electronics for same, an MMU, and enough interfaces to do whatever you want, be it plug in a USB keyboard and mouse, an Ethernet adapter, or a simple USB-to-serial converter circuit. An excellent example of a SoC is the Broadcom BCM2835, which forms the nucleus of the ultra-cheap RaspberryPi, which has become one of the most popular hardware platforms for hackers since the Arduino due to its low cost and the fact that it runs Debian GNU/Linux right out of the box. You can do almost everything with a RasPi that you can with a full-sized laptop or desktop machine. To be sure it has less RAM (512 megs on the high-end rev.B) than we're used to these days, but it's quite sufficient for such tasks as word processing, browsing the web, building multimedia entertainment centers, emulating other computers, home and vehicular automation, near Earth orbit launches... The RasPi's firmware, which we don't have the source code for is a sticking point of this platform. As has been mentioned previously, firmware blobs can potentially be doing anything and we wouldn't know unless the time was taken to reverse engineer them. The distributions of Linux and BSD that run on the RasPi seem to have a "whatever it takes" attitude toward getting the job done, and have incorporated code that loads the vendor-supplied firmware. This has caused several projects to flat out refuse to port their OSes to the RasPi. Another example of a commercial SoC is the Vortex86DX2, which is a 32-bit x86-compatible CPU that also incorporates USB, SATA, PCIe, Ethernet, JTAG, and several other peripherals and interfaces on a single chip. It runs at 800MHz and consumes only a hair over 2 watts of power. The downside is that it's closed source commercial product so you can't audit what might be going on inside the chip. Once again, if you bounce over to OpenCores' System On Chip page (note: that link goes to the projects page because there's no way to link to a specific category) you'll find a collection of open source SoC's that you can flash onto appropriate FPGAs and run with. I would also like to mention that a few hackers have re-implemented entire computers on single FPGAs, from the CPUs all the way to the graphics controllers and audio chipsets. Case in point the Suska, a stem-to-stern reimplementation of the Atari ST on a single chip. In 2012 the Open Source Hardware User Group of London held a seminar on how to implement an OpenRISC SoC on a £50 FPGA board, which demonstrates that doing so is entirely feasible for an emminently reasonable cost. There is also the ORPSoC (OpenRISC Reference Platform System on Chip), which combines an OpenRISC OR1200 CPU with a set of peripherals. A potential risk to the project is incurred in the the FPGAs themselves; some of the more powerful units have lots of processing power on board that could potentially have been subverted somewhere along the line. Caveat hacker. The trusted and open computer we are hypothesizing is going to need some peripherals so we can interact with it. At a minimum, we need a display, a keyboard, probably a mouse, and storage (volatile and not). If you are able to build your own high-res display comparable to those commercially available these days, please post your instructions so I can mirror them. So far as I know at this moment in time, constructing a display from scratch is probably not feasible. Using a different kind of display, like an older television with an RF modulator is possible but you might not get very high resolution graphics out of it. Even the RasPi's composite video output tops out at 720x576 (on a PAL television), though its HDMI output is considerably better. People like graphics. Going the text-only via serial terminal route is possible but, let's face it, nobody's going to do it. Depending on how hardcore one is, repurposing displays that are sufficiently simple that the circuitry can be eyeballed to determine that it was p