OCX files are components used in the Microsoft Windows operating system. They are essentially Dynamic Link Libraries (DLLs) that implement OLE (Object Linking and Embedding) controls, also known as ActiveX controls. These controls provide reusable functionality that can be embedded into various applications, such as Visual Basic, Microsoft Office applications, and web browsers (using plugins). OCX files contain code, resources (like icons and bitmaps), and metadata that define the control's properties, methods, and events. When an application uses an OCX control, it can interact with the control's functionality through its defined interface. OCX controls were a popular way to extend the capabilities of Windows applications and provide a consistent user interface across different programs. They are often used for tasks like displaying data, handling user input, and interacting with hardware devices. While OCX controls were widely used in the past, they have largely been superseded by newer technologies like .NET controls and other component-based architectures due to security concerns and compatibility issues with modern operating systems.