This document describes the design decisions made in building a simple hobbyist computer processor. The processor uses a 16-bit instruction word with a 4-bit opcode and 12-bit operand. It has a 4K word address space and operates on 12-bit data. The minimum instruction set includes arithmetic, logic, memory access, and program flow instructions. The data path includes registers to hold instructions and data, as well as an ALU and memory. In fetching and executing instructions, the program counter is incremented by the ALU to prepare for the next instruction fetch.