Summary
While it doesn’t feature that prominently in computer hardware advertising anymore, CPU (and GPU) clock speed is still an important factor to understand. For various reasons, the number alone doesn’t tell you much, but in some cases a higher clock speed can be the deciding factor when picking your parts.
Meet the CPU “Clock”
Inside a processor is a component known as a “clock generator”. This generates an electronic pulse at a specific frequency, which synchronizes the processes of the processor as a whole. With each clock “cycle” the CPU can perform a certain amount of work. So, if youincrease the frequencyof the pulses, all other things being equal, the CPU will get more work done.
Making Sense of Hertz
Clock speed is measured in Hz (Hertz) with one Hertz representing a single cycle per second. Early processors were slow enough to have speeds measured in Hertz, and then kilohertz(kHz), later megahertz (MHz), with modern processors typically running at multiple gigahertz (GHz). So one MHz is a million cycles per second, and a GHz is a billion cycles per second.
CPU Complexity vs Speed
So, a CPU with a higher clock speed is “faster” than another, lower-clocked CPU in the sense that it has more clock pulses per second. However, clearly, that can’t be the whole story, because CPU clocks haven’t really increased that much. If you look at the latest CPUs, some have lower clocks than models from last year, yet they will outperform them, and certainly a 3Ghz CPU from 2024 will run absolute circles around a 3GhzPentium 4 from the 2000s!
Firstly, the number of transistors and logical elements in a CPU makes a huge difference. The more “brains” a CPU has, the more work it can do in a single clock cycle. This is usually expressed as “instructions per clock” orIPC. If a new CPU has more IPC, it will perform better than an older CPU running at the same clock speed.
It’s also important to keep in mind that modern processors havemultiple cores. If two processors run at the same speed, but one has twice the same type of cores of the other, then the one with more cores can do way more work. This is complicated by the fact that not all software can take equal advantage of having more processor cores, but the principle should be clear.
There Are Multiple Clock Speeds
Muddying the waters of clock speed even more, CPUs have variable clock speeds. For example, if all of your CPU cores are engaged, they’ll run at a lower clock speed than if only one or two are engaged. This is to ensure that you’re getting the most out of the CPU regardless of what sort of software load is currently running.
Different components of the CPU may also run at different speeds. The CPU’s cache has its own speed, and in modern Intel CPUs with different CPU core types, the efficiency and performance cores have their own independent clock speed ranges. Likewise, your memory has its own clock and doesn’t run at the same speed as the CPU.
We Care About Performance, Not Frequencies
Back in the days of the so-called “Megahertz wars”, it was all about marketing the clock speed numbers of CPUs, which did have a huge impact on performance. Then CPU makers hit a wall, and started improving CPU performance in ways that are not related to making them run at higher frequencies. Today, looking at any part of a spec sheet simply won’t give you a clear idea of how well a CPU will perform.
We can look atFLOPs(Floating Point Operations) to get a precise idea of how much raw math a CPU can do, but even that’s not a perfect indicator of how well it will run software, especially with newer CPUs packing optimizations that make them more efficient at certain tasks.
In the end, what matters is how well a CPU performs in the software that you want to run, and looking for real-world testing and benchmarks remains the gold standard. With too many differences between even CPUs of the same generation and product stack, I personally don’t even bother looking at clock speeds when thinking about buying a new CPU, and in my opinion neither should most of you.
