This book is a collection of notes and sample codes written by the author while he was learning JVM himself. Topics include JVM (Java Virtual Machine) Architecture and Components; Oracle JVM implementation - HotSpot; Eclipse JVM implementation - Eclipse OpenJ9; java.lang.Runtime - The JVM Instance class; Loading Native Libraries; java.lang.System - Representing Operating System; java.lang.ClassLoader - Loading class files; java.lang.Class - Class reflections; Runtime data areas, heap memory and Garbage Collection; Stack, Frame and Stack overflow; Multi-threading impacts on CPU and I/O; CDS (Class Data Sharing); Micro Benchmark tests on different types of operations. Updated in 2024 (Version v5.13) with HotSpot JVM 20.For latest updates and free sample chapters, visit https://www.herongyang.com/JVM.