Gigahertz (GHz) s a frequency unit that measures the number of cycles per second.
Hertz (Hz) refers to the number of cycles per second with periodic 1-second intervals. A megahertz (MHz) equals 1,000,000 Hz. A gigahertz is equal to 1,000 megahertz (MHz) or 1,000,000,000 Hz.
Gigahertz is often used to measure central processing unit (CPU) clock speed. In general, higher CPU clock speeds indicate faster computers. That being said, speed-impacting factors include pipeline depth, instruction sets, internal cache, network/bus speed, disk performance and software design.
Techopedia explains Gigahertz (GHz)
One gigahertz equals 1,000,000,000 Hz or 1,000 MHz and has a frequency measurement with periodic 1-second cycles. A nanosecond is one-billionth of a second or one-thousandth of a microsecond. A nanosecond’s numeric order is 10 or 0.000000001.
Hertz is based on total rotations per second, that is, one full second rotation equals 1 Hz. One kilohertz represents 1000 rotations per second. One megahertz represents 1 million rotations per second. One gigahertz represents 1 billion cycles per second.
Clock speed, which is also measured in hertz, refers to synchronous circuit clock frequency, for example, a CPU. One clock lasts only 1 nanosecond and toggles between 0 and 1. Modern and non-embedded CPUs may have a single clock cycle of less than 1 nanosecond.
CPU megahertz usually refers to clock rate, frequency or speed. Clock rate is gauged by a crystal oscillator which generates highly accurate and unwavering electrical and clock signals; stabilizes receivers and frequencies; and tracks time. The oscillator circuit brings its crystal a small amount of electricity every nanosecond, which is measured in hertz.