The CPU may be a single chip or a series of chips that perform arithmetic and logical calculations and that time and control the operations of the other elements of the system. Miniaturisation and integration techniques made possible the development of the microprocessor, a CPU chip that incorporates additional circuitry and memory. The result is smaller computers and reduced support circuitry. Microprocessors are used in personal computers.

Most CPU chips and microprocessors are composed of four functional sections:

(1) an arithmetic/logic unit (ALU)

(2) registers;

(3) a control section;

(4) an internal bus.

The arithmetic/logic unit gives the chip its calculating ability and permits arithmetical and logical operations. The registers are temporary storage areas that hold date, keep track of instructions, and hold the location an results of these operations. The control section has three principal duties. It times and regulates the operations of the entire computer system; its instruction decoder reads the patterns of data in a designated register and translates the pattern into an activity, such as adding or comparing; and its interrupt unit indicates the order in which individual operations use the CPU, and regulates the amount of CPU time that each operation may consume.The last segment of a CPU chip or microprocessor is its internal bus, a network of communication lines that connects the interal elements of the processor and also leads to external conectors that link the processor to the other elements of the computer system.

The three types of CPU buses are:

(1) a control bus consisting of a line that senses input signals and another line that generates control signals from within the CPU;

(2) the address bus, a one-way line from the processor that handles the location of data in memory addresses;

(3) the data bus, a two-way transfer line that both reads date from memory and writers new data into memory.