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Direct3D is a graphics application programming interface (API) developed by Microsoft that functions under the larger DirectX suite. It is utilized for rendering three-dimensional graphics in applications where performance is a critical component, like games. It provides a higher level of hardware abstraction than OpenGL, another widely-used graphics API, and as a result, can offer advanced features and high performance for Windows-based systems.

Direct3D interfaces with the graphics hardware in the system, creating a consistent platform for developers. This means that developers can create complex graphics without needing to understand the intricacies of the hardware. The API contains a myriad of features to facilitate rendering, including shaders, transformations and lighting models. Direct3D's depth buffer for example, automatically calculates which objects are in the foreground and which should be shaded, keeping track of every pixel in the current frame and its corresponding depth value.

One significant advantage of Direct3D is its versatility, facilitated by its ability to operate at either high-level or low-level interface. On the high-level side, it offers simple tools for managing hardware resources, as well as facilitating common tasks such as geometry management and material application. At the low-level access, it allows more direct control of the graphics pipeline. This makes it a flexible tool, as it caters for developers requiring both abstraction and those needing explicit control for optimization.

Direct3D is integral to various popular high-intensity applications and games, and this can be attributed to it being on the leading edge of graphics technology progress. The API is regularly updated with new iterations featuring advanced capabilities, like the addition of ray tracing in Direct3D 12, an algorithm used to trace the path of rays of light to render high-quality three-dimensional visuals.

However, despite these advantages, using Direct3D as a graphic development tool does have some downsides. It can be complicated to understand and use considering the highly technical nature of the work it performs. The API has also seen criticism for its constantly changing specifications and requirements for programmers, with each version bringing a different method of use.

In summary, Direct3D is an advanced graphics API that provides both abstraction and direct control. It's integral to the creation of complex, high-performance 3D graphics, particularly on Windows-based systems. Microsoft's regular updates ensure it stays relevant, although the constant changes can cause difficulties for developers.