Backwardcompatibility

Backward compatibility, also known as compatibility with older versions, is a property of a system that allows newer versions to work with artifacts created for earlier versions. This can apply to software, hardware, data formats, and interfaces. In software, backward compatibility means that programs or components written for an older version continue to function when run on newer versions, or that data created by older software remains readable.

There are several notions: binary or ABI compatibility, source compatibility, and API compatibility. Binary compatibility ensures that compiled code can link with and run under a newer runtime or library without recompilation; source compatibility means that old source code can be rebuilt with a newer toolchain; API compatibility guarantees that public interfaces remain stable across releases.

Strategies to achieve backward compatibility include maintaining stable public interfaces, providing deprecation periods, offering compatibility shims or adapters, and using version-aware runtime environments or feature flags. Design choices often involve trade-offs between backward compatibility and modernization, openness to breaking changes, and maintenance burden.

In practice, backward compatibility helps protect user investments and ecosystems but can hinder innovation if older interfaces constrain new design. It is supported by testing regimes such as regression tests and compatibility suites, along with documented deprecation schedules and long-term support cycles.

Examples span programming languages, operating systems, and hardware platforms. Many ecosystems strive to preserve backward compatibility across releases, while occasionally signaling breaking changes through major versions or documented deprecations.