Information from an input device or memory is communicated via the bus to the CPU, which is the part of the computer that translates commands and runs programs. The CPU is a microprocessor chip-that is, a single piece of silicon containing millions of electrical components. Information is stored in a CPU memory location called a register. Registers can be thought of as the CPU's tiny scratchpad, temporarily storing instructions or data. When a program is run, one register called the program counter keeps track of which program instruction comes next. The CPU's control unit coordinates and times the CPU's functions, and it retrieves the next instruction from memory. In a typical sequence, the CPU locates the next instruction in the appropriate memory device. The instruction then travels along the bus from the computer's memory to the CPU, where it is stored in a special instruction register. Meanwhile, the program counter is incremented to prepare for the next instruction. The current instruction is analyzed by a decoder, which determines what the instruction will do. Any data the instruction needs are retrieved via the bus and placed in the CPU's registers. The CPU executes the instruction, and the results are stored in another register or copied to specific memory locations.
