A computer contains many components that share the same data pathway, called the "system bus." Because the computer's processor, memory, video card and other components all operate at different speeds, a system clock governs the timing with which these components transfer data, so that the system bus is used as efficiently as possible. The speed of a computer's system bus is measured in hertz, or the number of clock cycles each second. The processor's speed is a multiple of the system bus speed, expressed in billions of cycles per second or gigahertz (GHz).
Measuring Computer Performance
Computer manufacturers primarily use "GHz" as a marketing term to describe the relative performance of the different computers they offer. If two computers are similar in design and share the same processor architecture, the computer with a higher processor clock speed in GHz will offer superior performance. However, several other factors also influence overall computer performance, such as the speed of the video card, memory and hard drive.
Breaking the GHz Barrier
Processors with speeds exceeding 1 GHz were first made available to consumers in 2000. Within days of each other, Intel shipped the 1 GHz Pentium III processor and AMD released the 1 GHz Athlon processor. According to ZDNet, both companies claimed to be the first to market a gigahertz processor. AMD broke another clock speed barrier in 2013 with the release of the FX-9000 processor series, the fastest of which could operate at 5 GHz under air cooling.
The Impact of CPU Architecture
Computer manufacturers often place emphasis on the GHz rating of their computers' processors because most consumers have a basic understanding of what the term means. However, a higher GHz rating doesn't necessarily mean a faster processor. As the clock speed of a processor increases, the processor generates more heat and requires more power to remain stable during operation. With desktop computers already drawing more than 100 watts of power in an idle state, processor makers have focused on increasing the efficiency of their designs. Multiple cores, for example, give processors the ability to execute several instructions simultaneously, increasing their performance without raising clock speed. Processors made by Intel and AMD differ so greatly in design that they cannot be compared on the basis of clock speed alone. Computer enthusiasts use standardized tests called "benchmarks" to measure the performance of dissimilar processors.
Overclocking for More GHz
In some cases, it may be possible to configure a computer's processor so it runs faster than its rated GHz speed. This usually requires entering the computer's BIOS configuration menu to increase the speed of the system bus -- which forces all of the system's components to run at a faster speed -- or the "CPU multiplier," which increases the speed of the processor alone. Overclocking generally voids a computer's warranty and may shorten the usable life of its components. However, many enthusiasts overclock their computers anyway to improve performance during gaming, video rendering and other tasks. Using "extreme cooling" methods such as liquid nitrogen, it is possible to temporarily achieve processor speeds above 8 GHz.