From: https://www.quora.com/What-is-the-difference-between-an-MCU-a-CPU-and-a-GPU-Are-they-interchangeable-terms-for-different-parts-in-computers-What-are-their-uses

An MCU (microcontroller unit), CPU (central processing unit), and GPU (graphics processing unit) are all different types of processors, but they are not interchangeable terms.

MCU: An MCU is a type of processor that is designed for embedded systems and other applications that require a small, low-power device. It typically includes a CPU, memory, and I/O peripherals on a single chip. MCUs are used in a wide range of applications, including consumer electronics, automotive systems, and industrial automation.

CPU: A CPU is a general-purpose processor that is designed to perform a wide range of tasks, including running operating systems, running applications, and performing complex calculations. It is the "brain" of a computer or other electronic device, and is responsible for executing instructions and managing the system's resources.

GPU: A GPU is a specialized processor that is designed for parallel processing of graphics data. It is optimized for tasks such as rendering 2D and 3D graphics, video encoding and decoding, and scientific computing. GPUs are commonly used in gaming systems, workstations, and supercomputers.

While all three types of processors have their own unique strengths and applications, they are not interchangeable. An MCU is optimized for low-power and low-cost applications, while a CPU is designed for general-purpose computing, and a GPU is designed for parallel processing of graphics data.

In summary, MCUs are typically used in embedded systems, CPUs are used in a wide range of general-purpose computing applications, and GPUs are used for specialized tasks such as graphics rendering and scientific computing.