What is the SAT?   The SAT is a three-hour - and- 45 minute test that measured critical reading, mathematical reasoning, and writing skills that students have developed over time and need to be successful in college.

What are the SAT II subject tests?  Subject tests are one-hour, primarily multiple-choice tests that measure your knowledge of particular subjects and your ability to apply that knowledge.  Check the requirements of the colleges you're considering.  Many require or recommend one or more Subject Tests for admission or placement.