First, we need to create a matrix that will represent Sudoku puzzle as an Exact Cover problem. The matrix will have 9^3 rows, i.e., one row for every single possible position (9 rows x 9 columns) of every possible number (9 numbers). Columns will represent the board (again 9 x 9) multiplied by the number of constraints. Welcome to Operating Systems: Three Easy Pieces (now version 1.00 -- see book news for details), a free online operating systems book! The book is centered around three conceptual pieces that are fundamental to operating systems: virtualization, concurrency, and persistence. In understanding the conceptual, you will also learn the practical.