Brickyard is a design for a simple (simulated) personal computer environment, to be used for OS development. It presents a highly simplified and idealized set of hardware (display, input, storage) to the CPU, so that people interested in OS development can focus on writing critical OS features like scheduling, interrupt handling, and memory management, without having to wade through the complexities of modern (or classical) hardware.
Brickyard will use a MIPS32 CPU. This means that it will have to be emulated on almost all target platforms. However, even if ARM or x86 were selected, emulation would still be necessary on the "other" platform, and even on the host platform, highly platform- and OS-specific code would be necessary to allow for the needed degree of virtualization. Given that emulation is almost a requirement, MIPS was selected because it is easier to write emulators for than ARM or x86, but it still has a full GNU toolchain available.
A 32-bit CPU is used so that emulat