# Overview of ArkTS Runtime

ArkTS Runtime is the default language runtime for applications on OpenHarmony. It executes bytecode and standard libraries for ArkTS, TS, and JS languages, and supports the interpreter, Ahead-of-Time (AOT), and Just-In-Time (JIT) for efficient execution. It also provides [Node-API](../napi/napi-introduction.md) to enable multi-language hybrid development. 

ArkTS Runtime is primarily composed of four subsystems:

- **Core subsystem**: consists of the foundational runtime libraries that are language-agnostic, including the File component that carries bytecode, the Tooling component that supports Debugger functionality, and the Base library component responsible for adapting system calls.

- **Execution subsystem**: includes the interpreter for executing Ark bytecode, fast-path inline caches, and [file-based modular management for runtime execution](module-principle.md).

- **Compiler subsystem**: includes the stub compiler, an IR-based compilation optimization framework, an AOT static compiler, and an experimental JIT dynamic compiler.

- **Runtime subsystem**: includes the following modules related to the execution of ArkTS/TS/JS:

  - Memory management: object allocator and [garbage collector](gc-introduction.md) (CMS-GC and Partial-Compressing-GC for concurrent marking and partial memory compression)

  - Analysis tools: DFX, and profiling tools for CPU and heap analysis

  - Concurrency management: Ark bytecode file manager in the actor model

  - Standard libraries: standard libraries defined by ECMAScript, efficient container libraries, and object models
  
  - Other: asynchronous work queues, and Node-API that interact with C++