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GHz

Hardware

GHz (Gigahertz) is a unit of frequency equal to one billion cycles per second. In computing, GHz most commonly describes CPU clock speed—how many cycles the processor completes each second. A 3.5 GHz processor completes 3.5 billion cycles per second. The lesson What Is a System Clock? explains how this clock drives instruction execution in the CPU.

Why it matters

Clock speed is one factor in CPU performance, but as the lesson Why Some Computers Feel Faster explains, raw GHz doesn't tell the whole story. Modern processors do more work per cycle than older ones, so a 3.0 GHz processor today can be much faster than a 3.0 GHz processor from 2010. Understanding GHz helps you interpret processor specifications while recognizing that other factors—like architecture, core count, and cache—also matter significantly.

Clock speed and performance

Each clock cycle lets the CPU perform operations: fetching instructions, performing calculations, moving data. Higher clock speeds mean more cycles per second, which generally means more work done. However, different CPU architectures accomplish different amounts of work per cycle. An ARM processor and an x86 processor at the same GHz will have different real-world performance.

Frequency units

GHz is part of a family of frequency measurements:

  • Hz (Hertz): 1 cycle per second
  • MHz (Megahertz): 1 million cycles per second (1,000,000 Hz)
  • GHz (Gigahertz): 1 billion cycles per second (1,000 MHz)

CPUs evolved from MHz (early Pentiums ran at 60-200 MHz) to GHz in the early 2000s. Modern desktop CPUs typically run between 3-5 GHz, with "boost" speeds reaching higher for short bursts when thermal headroom allows.

Beyond clock speed

RAM also has speed ratings in MHz (like DDR4-3200, which transfers at 3200 MHz), and wireless technologies like Wi-Fi use GHz to describe radio frequencies (2.4 GHz and 5 GHz bands). The unit always means the same thing—cycles or oscillations per second—but applies to different contexts.

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Further reading