GHz/MHz

In short: Gigahertz and megahertz — units of measurement for frequency, i.e. oscillations or cycles per second. 1 GHz = 1,000 MHz = 1 billion cycles per second.

In more detail: In IT, these units are mainly encountered for CPU clock rates and RAM speeds (e.g. DDR5-6000 = 6,000 MHz effective clock rate). Important: a higher number is only directly comparable within the same architecture/generation, not across different chip generations.

In Depth

The physical basis

Hertz (Hz) is the basic physical unit for frequency: one hertz corresponds to one complete oscillation cycle per second, named after the physicist Heinrich Hertz. For electronic components, the clock frequency states how many such cycles the internal clock generator (usually a quartz oscillator as a precise time reference) delivers per second — each cycle is basically a “tick” at which the circuit can perform a defined step of work. A higher frequency therefore fundamentally means more possible steps of work per second, but also more generated waste heat (power dissipation rises disproportionately with frequency), which is why frequency can never be increased indefinitely without cooling growing accordingly.

Real vs. effective clock rate for RAM

The distinction between real and “effective” clock rate is important, and often causes confusion with RAM specs: DDR memory (Double Data Rate) transfers two data packets per clock cycle instead of one, which is why manufacturers state the effective, doubled data rate (e.g. “DDR5-6000” effectively means 6,000 MT/s — megatransfers per second — while the real internal clock is only 3,000 MHz). This doubling happens by transferring data on both the rising and falling signal edge, instead of only once per complete cycle.

Why GHz comparisons can be misleading

For CPU clock rates, in addition: a direct comparison of the GHz number is only really meaningful within the same chip architecture and generation — a newer, more efficient CPU generation can still do more work per second at a lower clock speed than an older one with a higher clock number, because it processes more instructions per clock cycle (“instructions per clock”, IPC). A pure GHz comparison between, say, a 5-year-old CPU and a current model therefore says practically nothing about actual relative performance.

Frequency figures outside the CPU

GHz/MHz figures are also encountered outside the CPU and RAM: for Wi-Fi frequency bands (2.4 GHz, 5 GHz, more recently 6 GHz), for radio frequencies in general, or for the clock rate of bus systems like PCIe. In all these contexts, the unit denotes the same physical principle — oscillations/cycles per second — applied to very different technical contexts.

See also: Clock speed (GHz), RAM, CPU