Definition: MHz

(MegaHertZ) One million cycles per second. MHz is used to measure the transmission speed of electronic devices, including channels, buses and the computer's internal clock. A one-megahertz clock (1 MHz) means some number of bits (1, 4, 8, 16, 32 or 64) can be manipulated at least one million times per second. A two-gigahertz clock (2 GHz) means at least two billion times. The "at least" is because multiple operations often occur in one clock cycle.

Both megahertz (MHz) and gigahertz (GHz) are used to measure CPU speed. For example, a 1.6 GHz computer processes data internally (calculates, compares, copies) twice as fast as an 800 MHz machine.

Why Isn't It Faster?
A CPU in the new computer billed as twice the MHz or GHz as the previous computer does not mean twice as much finished work gets done in the same time frame. Internal cache and CPU architecture plus the speed of the RAM, storage and network all contribute to the computer's actual performance and overall throughput. See cache.

Users are often dismayed to find only incremental improvements after purchasing a so-called "faster" computer. In addition, newer versions of software are sometimes slower than previous versions, and a faster computer is often required just to maintain the same performance level as the old software. See instructions per second, Hertz and space/time.

MHz and GHz Are the Heartbeat
When referencing CPU speed, MHz and GHz rate the raw, steady pulses that energize the circuits in a chip. The German physicist Heinrich Hertz identified electromagnetic waves in 1883, and coincidentally, "Herz" in German means "heart."

Speed and Width

Megahertz (MHz) and gigahertz (GHz) are the CPU's clock speed, and the number of bits (8, 16, etc.) are the width of the CPU's registers. The combination of speed and width determines the inherent processing performance of the CPU chip. Parallel channels from the CPU to external devices are also measured by speed and width; however, serial channels are rated only by speed. See parallel transmission, serial transmission and PC data buses.