When I’m shopping for a desktop computer, I hear two numbers constantly: Clock speed (usually in GHz) and core/thread count. What else is there to CPU performance besides these two numbers? What makes a modern CPU more performant than a CPU from years ago, assuming the same core count and clock speed?
A CPU, at its basic level, does math and logic. GHZ is a measure of electrical frequency, aka how fast the switches inside a CPU turn on and off per second; it is only tangentially, loosely related to the amount of math and logic per second that the CPU can do.
Like the other commenter said, IPC, or instructions per clock, measures how much “stuff” a CPU can do each time it’s control signal switches on and off. More advanced modern CPU’s can do more stuff per clock, both because of architecture improvements, and because there are more “cores” (CPU’s inside the CPU, basically). And because of the difference in architecture and other behaviors, it’s hard to “apples to apples” compare CPU’s. I could take a 4 core cpu from 2012 and a 4 core cpu from today, have them both run at 4ghz, and the modern one would run circles around the 2012 cpu.
The better way to shop for modern processors is not to look at nameplate numbers like GHz. Instead you should find multiple independent software benchmarks that can apply a relative number to the amount of math and logic a CPU can do per second, which allows you to accurately compare different processors side by side. Software like Cinebench does this. There are multiple artificial benchmarks that show performance in many different workloads, pick one out that is most similar to what you would do on a daily basis.
Many review sites like tomshardware will also provide additional data, like core temperatures and power consumption under load, to provide a fuller image of what a CPU can do and what its drawbacks might be.