24/12/2025
Runtime vs Virtual Machine — Understanding the Ex*****on Layer
We often see runtime and virtual machine used as if they mean the same thing — but they don’t.
A runtime is the complete environment where a program executes.
It may run native machine code, manage memory, handle scheduling or event loops, and interact with the operating system. A runtime may include a virtual machine, but it doesn’t have to.
A virtual machine (VM) is a specific component that executes non-native instructions such as bytecode. It abstracts the CPU and often compiles instructions to native code, but relies on the runtime for OS-level interactions.
Key idea:
A VM can be part of a runtime, but a runtime is more than just a VM.
Understanding this distinction helps clarify how Java, JavaScript, .NET, and other platforms actually run programs.