Clock speed, also known as a “clock rate”, indicates how fast a processor executes a given instruction. Each CPU needs a fixed number of clock ticks, or cycles, to execute an instruction. A higher clock speed, or clock rate, means that a processor can perform more instructions per second. The measurement is “clock cycles per second”, with the SI equivalent being Hz. Even though initially, you would’ve found CPU frequencies advertised in kHz, today’s CPUs are advertised in GHz (Gigahertz).
How is clock speed determined?
With each CPU, the clock speed is determined by a crystal oscillator’s frequency. That crystal oscillator produces a fixed sine wave, which is then translated into a square wave. On any CPU, if you were to replace the oscillator with one that oscillates at half the frequency, you’re making the whole CPU run at half of its performance. If it operates at a higher frequency, the CPU is faster. The amount of speed modifications you can do, however, also depends on how much time the CPU needs to settle after each pulse, as well as the dissipation of any extra heat created in the process.
There’s also the process known as binning, where manufacturers charge more for processors that can operate at higher clock rates. This refers to both CPUs and GPU processors. For any given CPU, the clock speed is at the end, though actual testing. Each chip must meet the maximum clock speed specification. Processors that meet the specification are often labeled with a higher clock speed, while those that don’t may be sold at a lower price, with a lower clock speed.
How much of an impact does clock speed have on performance?
The clock speed directly impacts a CPU’s speed, and consequently, the performance. You’ll notice the largest impact in programs and applications that are made to utilize a single core. A higher clock speed on an otherwise identical processor may make a noticeable difference in performance.
However, clock speed can also be very deceiving and should by no means be your number one metric for choosing a CPU. This is because the pipelining efficiency and number of instructions per clock cycle from one CPU manufacturer to another may vary drastically. Therefore, though the clock speed of one CPU may be higher than another, it doesn’t mean that the CPU with the higher clock speed is necessarily faster or more efficient.
If you’re comparing processors from the same family, which are otherwise identical, the clock speed does have an impact. A good example would be Intel’s Core i7-8550U, which has a maximum turbo clock speed of 4.0GHz, whereas the i7-8565U is identical in everything else yet has a maximum turbo clock speed of 4.6GHz, making it effectively around 30% faster in single threaded applications.
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