Heavy highlighting and passive re-reading feel productive, but they fail when it counts. The Study OS is an evidence-based study system built around active recall, spaced repetition, practice testing, and better calibration of what you actually know. Backed by cognitive research showing that retrieval practice drastically outperforms repeated study on delayed tests, this guide gives medical students and ambitious learners a repeatable system to turn raw notes into retrieval prompts, close knowledge gaps, and make memory survive time.