CPU architectures refer to the design and organization of a computer's central processing unit (CPU). This includes how the CPU processes instructions, manages data, and communicates with other components. Common architectures include x86, used in most personal computers, and ARM, which is popular in mobile devices due to its energy efficiency. Different CPU architectures can impact performance, power consumption, and compatibility with software. For example, RISC (Reduced Instruction Set Computing) architectures focus on a small set of simple instructions, while CISC (Complex Instruction Set Computing) architectures have a larger set of more complex instructions. Each architecture serves specific needs and applications.