Clock and Bus Speeds

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The motherboard contains an oscillating system crystal, or oscillator. This built-in timer or clock controls the speed at which the CPU can transfer information to and from memory, and communicate with peripheral devices. Clock speed is normally expressed in megahertz (MHz). For example, if you have a 550MHz Pentium III processor, the clock speed is 550MHz. One megahertz is equal to 1 million cycles per second of the oscillating clock. The clock speed on the motherboard can be configured with little plastic jumpers located on the motherboard itself. Most motherboards are designed to run at multiple clock speeds. It is important to set the CPU and other motherboard components to run at the maximum clock speed of the motherboard; the wrong settings can result in an overheated processor. Also, if a processor fan on top of your processor is being used for cooling purposes, every so often you should verify that it is working properly. If it has failed, the system may lock up, and the processor may suffer irreversible damage due to overheating.

Looking at a motherboard, you can see little pathways that lead from component to component. These pathways are actually tiny wires that carry information from place to place. These wires make up the system bus. Bus speed is measured by the width of the bus. The width of the bus is calculated by the number of bits of information the bus can move at a given time. The actual speed of the bus is provided in the form of megahertz. Typical bus widths are 16, 32, and 64 bits. Most systems today have 64-bit-wide buses that run at 100MHz. There are newer chipsets on the market that run at 133MHz.

The External Data Bus

The external data bus is made up of tiny wires integrated into the motherboard that the CPU uses as a means to communicate with peripheral devices.

The Address Bus

The CPU uses the address bus, which is also made up of tiny wires integrated into the motherboard, to access areas of memory by the Memory Controller Chip (MCC). The address bus keeps track of locations in memory called memory addresses. The number of memory addresses in a system is based on the size, or ‘width,' of the address bus.

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