The Motherboard

The motherboard is where the computer's primary electronic circuitry resides. This is a printed circuit board that contains a number of electronic components which perform the processing, storage, and some routing and control steps. Note the row of connections on the motherboard; these are called expansion slots, into which other printed circuit cards are plugged. They provide electrical connections from the processor to other hardware components, as we shall see. Note also the connectors at the rear of the motherboard. These are called ports, or interfaces, to which cables are connected for peripherals such as the keyboard, monitor, and printer.

Among the electronic components on the motherboard are a number of integrated circuits. An integrated circuit (С) has hundreds, often thousands, of electronic circuits in a single piece of silicon, which is housed in a casing with a number of tiny electrical connections or "feet". The large black square on the motherboard is one type of integrated circuit; it is the processor chip, or what we call the CPU.

The CPU

The central processing unit (CPU) is the computer's brain. As its name implies, it is where the processing step takes place. Instructions are executed and data is processed. The CPU consists of three components: the control unit, the arithmetic/logic unit, and main memory. The personal computer's CPU is commonly a single chip; in larger computers, it may be many chips.

The control unit directs the step-by-step operation of the computer. Like a traffic policeman at a busy intersection, the control unit directs electrical impulses between itself, the ALU, and storage. It also controls operations between the CPU and the peripheral devices. These electrical impulses consist of instructions and the data being processed.

The arithmetic/logic unit (ALU) performs the arithmetic and logical operations. You'll recall that the arithmetic operations are addition, subtraction, multiplication, and division. The logic operations compare two pieces of data to determine if one is greater than, less than, or equal to the other.

Random access memory (RAM), also called main memory, is the third component of the computer's CPU. RAM carries out the storage step for the CPU, providing temporary storage for the programs being executed and for data as it passes through processing. RAM is short-term, volatile memory; that means everything stored there is lost when the computer's power is shut off. RAM is not a physical part of the CPU chip. Rather, it is made up of a number of additional chips electrically connected — what is termed logically connected—and in close proximity to the CPU chip. This can be seen in the rows of RAM memory chips installed beside the CPU, and the arrows indicat­ing the flow of data within the CPU and between the CPU and main memory.

There is another type of memory associated with the CPU called read only memory (ROM). It is memory chips that are used to store permanent instruc­tions that perform many routine tasks for the CPU; these instructions cannot be changed.

The motherboard, is the most important single hardware component. It contains all the circuitry for the CPU, control and routing components, and short-term storage. However, it is not the only component in the system unit. The power supply provides the proper electricity to each component. The cooling fans do just what the name implies, moving cooling air across the electronic components.

Knowledge Check

1. What do we call the portion of the computer that we can touch? 2. Where does the computer's primary electronic circuitry reside?

3. What does CPU stand for?

4. What two units make up the CPU?

5. What is volatile memory?

6. How does ROM differ from RAM?