What question did this study set out to answer?

The aim is to identify which changes to DLL and COM components break their callers, focusing on compatibility layers.

July 29, 2026Open Access

DLL and COM Interface Backward Compatibility — A Decision Table for Which Changes Break Callers (archived 2026-07-27)

Key Points

The aim is to identify which changes to DLL and COM components break their callers, focusing on compatibility layers.
Organized compatibility into three layers: binary, source, and behavioral.
Presented a decision table based on the type of changes made.
Provided a practical guide on implementing semantic versioning (semver).
Established the iron rule that COM interfaces must not change to maintain compatibility.
Highlighted various change types that impact binary, source, and behavioral compatibility.
Emphasized the importance of a structured approach for developers managing DLL and COM interfaces.

Abstract

Which changes to a DLL or COM component actually break their callers? We lay out the three layers of compatibility — binary, source, and behavioral — a decision table organized by kind of change, the iron rule that COM interfaces never change, and a practical guide to running semver. Archived version of https://comcomponent.com/en/blog/dll-com-interface-backward-compatibility/, as published on 2026-07-27. The live article is maintained and may change after this date. First published 2026-07-17.

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