OSTEP (“oh step”), or the “the comet book”, represents the culmination of years of teaching intro to operating systems to both undergraduates and graduates at the University of Wisconsin-Madison Computer Sciences department for nearly 20 years.The book is organized around three concepts fundamental to OS construction: virtualization (of CPU and memory), concurrency (locks and condition variables), and persistence (disks, RAIDS, and file systems).The material, if combined with serious project work and homeworks, will lead students to a deeper understanding and appreciation of modern OSes.The authors, Remzi and Andrea Arpaci-Dusseau, are both professors of Computer Sciences at the University of Wisconsin-Madison.