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In computing, "runtime" refers to the period a program is executing, or the supporting software environment required for that execution. It is the time a program is running on a computer, from when it starts until it is closed, where the CPU executes machine code instructions. The term also describes the "runtime environment," which includes the operating system and necessary code libraries that allow the program to function, like handling memory or making system calls.

Key aspects of runtime

Execution time: This is the most common meaning, referring to the duration a program is active on a computer.

Runtime environment: The environment a program runs in, consisting of the operating system and any additional software needed for execution.

Examples include:

Dynamic-link libraries (DLLs): Code libraries that programs call on for standard functions.

Virtual machines (VMs): Programs like the Java Virtual Machine that provide a platform for running code.

Runtime system: The collection of software that supports the execution of programs, handling tasks like memory management, error handling, and implementing language features.

Runtime error: A bug or problem that occurs while the program is running, as opposed to a syntax error that is caught during compilation.

Container runtime: In cloud-native environments, this specifically refers to the software that manages containers, handling tasks like unpacking, mounting, and executing container images.