This is a system:

Input -> [System]
[System] -> Output
[System] <-down-> State

System has an Input, Output, State, Boundary, and Environment.

Layered System

Systems are often layered on top each other. Layered systems are also called stacks.



  • MITM, interception at the boundary

Runtime System

Runtime system provides the environment in which other software is executed.

The runtime system is defined primarily by the operating system and by the language platform.

Runtime is a Layered System:

  • Software is supported built on top of its language

  • The language may be built on top multi-language platform runtime

  • The language platform runtime is built on top of the operating system

  • The operating system operates on top of the hardware system


All user space software operates on top of operating system kernel.