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(1) A periodic signal generated by hardware for activation and/or synchronization purposes. See MHz.

(2) A periodic signal generated by hardware or software to indicate that it is still running.


(MegaHertZ) One million cycles per second. It 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 two times faster than the old computer does not mean twice as much finished work gets done in the same time frame. Internal cache design, bus speed, disk speed and network speed all contribute to the computer's actual processing speed and performance (the overall throughput).

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 MIPS, Hertz and space/time.

MHz and GHz Are the Heartbeat
When referencing CPU speed, the megahertz and gigahertz ratings are really the heartbeat of the computer, providing the raw, steady pulses that energize the circuits. If you know German, it is easy to remember. The word "Herz," pronounced "hayrtz," means heart. This was a coincidence, because in 1883, Heinrich Hertz identified electromagnetic waves.

Speed and Width
Just like a faster, wider highway handles more traffic, megahertz and gigahertz are the CPU's clock speed, and the number of bits (8, 16, 32, 64) are the width of the CPU's registers. The combination of the two determines the inherent processing speed of the CPU chip; however, there are many more factors after that. Clock speed and channel width also determine the transmission speed of pathways within a chip or from a chip to external devices (see PC data buses).

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