The heart of a computer is a device referred to as the Central Processing Unit (Often abbreviated CPU). The CPU is the physical device where all the fancy processing we talked about in the essentials of computing happens. Every other device attached to a computer system eventually sends information to or receives information from the CPU. The basic kinds of instructions (like the add, store, jump instructions we played with earlier) are built into the CPU. The characteristics of the CPU determine what kind of computer you have.