The device that interprets and executes instructions in a computer is the CPU (Central Processing Unit). Often referred to as the brain of the computer, the CPU performs calculations and manages data flow between various components like memory and storage. It processes instructions from programs by fetching data, executing operations, and storing results. Modern CPUs contain multiple cores, allowing them to handle several operations simultaneously, enhancing overall performance and efficiency. The CPU's speed, measured in gigahertz (GHz), significantly influences a computer's processing capabilities and responsiveness.