Product Code Database
Clock rate or clock speed in computing typically refers to the frequency at which the clock generator of a Microprocessor can generate Clock signal used to synchronize the operations of its components. It is used as an indicator of the processor's speed. Clock rate is measured in the SI unit of frequency hertz (Hz).
The clock rate of the first generation of computers was measured in hertz or kilohertz (kHz), the first personal computers from the 1970s through the 1980s had clock rates measured in megahertz (MHz). In the 21st century the speed of modern CPUs is commonly advertised in gigahertz (GHz). This metric is most useful when comparing processors within the same family, holding constant other features that may affect performance.
After each clock pulse, the signal lines inside the CPU need time to settle to their new state. That is, every signal line must finish transitioning from 0 to 1, or from 1 to 0. If the next clock pulse comes before that, the results will be incorrect. In the process of transitioning, some energy is wasted as heat (mostly inside the driving transistors). When executing complicated instructions that cause many transitions, the higher the clock rate the more heat produced. Transistors may be damaged by excessive heat.
There is also a lower limit of the clock rate, unless a fully static core is used.
The first commercial PC, the Altair 8800 (by MITS), used an Intel 8080 CPU with a clock rate of 2 MHz (2 million cycles per second). The original IBM PC (c. 1981) had a clock rate of 4.77 MHz (4,772,727 cycles per second). In 1992, both Hewlett-Packard and Digital Equipment Corporation (DEC) exceeded 100 MHz with RISC techniques in the PA-7100 and AXP 21064 DEC Alpha respectively. In 1995, Intel's P5 Pentium chip ran at 100 MHz (100 million cycles per second). On March 6, 2000, AMD demonstrated passing the 1 GHz milestone a few days ahead of Intel shipping 1 GHz in systems. In 2002, an Intel Pentium 4 model was introduced as the first CPU with a clock rate of 3 GHz (three billion cycles per second corresponding to ~ 0.33 per cycle). Since then, the clock rate of production processors has increased more slowly, with performance improvements coming from other design changes.
Set in 2011, the Guinness World Record for the highest CPU clock rate is 8.42938 GHz with an Overclocking AMD FX-8150 Bulldozer-based chip in an Liquid helium/Liquid nitrogen cryobath, 5 GHz Air cooling. This is surpassed by the CPU-Z overclocking record for the highest CPU clock rate at 8.79433 GHz with an AMD FX-8350 Piledriver-based chip bathed in Liquid nitrogen, achieved in November 2012. It is also surpassed by the slightly slower AMD FX-8370 overclocked to 8.72 GHz which tops off the HWBOT frequency rankings. These records were broken in 2025 when an Intel Core i9-13900KF was overclocked to 9.12 GHz.
The highest boost clock rate on a production processor is the Raptor Lake, clocked at 6.2 GHz, which was released in Q1 2024.
The first fully reversible CPU, the Pendulum, was implemented using standard CMOS transistors in the late 1990s at the Massachusetts Institute of Technology.
Engineers also continue to find new ways to design CPUs so that they complete more instructions per clock cycle, thus achieving a lower CPI (cycles or clock cycles per instruction) count, although they may run at the same or a lower clock rate as older CPUs. This is achieved through architectural techniques such as instruction pipelining and out-of-order execution which attempts to exploit instruction level parallelism in the code.
The clock rate alone is generally considered to be an inaccurate measure of performance when comparing different CPUs families. Software benchmarks are more useful. Clock rates can sometimes be misleading since the amount of work different CPUs can do in one cycle varies. For example, superscalar processors can execute more than one instruction per cycle (on average), yet it is not uncommon for them to do "less" in a clock cycle. In addition, subscalar CPUs or use of parallelism can also affect the performance of the computer regardless of clock rate.
|
|
