Windows can make a few adjustments but mostly it goes by the baseclock speed and multiplier set in the BIOS.
Unless you have the right CPU and right chipset on your motherboard, you can't touch this setting. You would basically have to build a computer if you want to adjust this yourself.
The wrong part you're talking about isn't wrong. The CPU multiplier decreases when there isn't a good workload to push it to it's maximum speeds. The multiplier drops in order to save power. This may not be an issue in certain parts of the United States but in Europe this is a lifesaver because their electricity is expensive.
Windows doesn't know the speed of your CPU… unless you're talking about the old benchmarks in the "experience index"
If you're talking about GHz, it can changes as the CPU needs. There can also be driver errors, many hardware programs will have them, I'd suggest using a 3rd part program to look up the info you need on your CPU.
Some monitoring programs will offer a bad reading. This, more often than not is true with AMD processors which offer different information.
If you have an AMD processor you should use AMD Overdrive.
If you use an Intel CPU uou should use https://www.piriform.com/speccy/download
I use an Intel processor so I use speccy https://s5.postimg.org/fv7qpn0mv/4690_K….
You can also use Hwmonitor, Coretemp, Speedfan and more than a few other monitoring programs. For GPUs MSI Afterburner is one of the more popular monitoring programs for gamers. It allows a gamer to see in real time the condition of their PC https://postimg.cc/image/3li74o6b7/ . I had but a small handful of resources chosen to show in the OSD. It does however allow us to see temperatures, loads, fan speeds and so much more. EVGA PrecisionX 16 and Asus GPU Tweak are a couple other monitoring programs for GPUs.
I can tell you for a fact The programs I mentioned, when used with the right CPU aren't usually wrong with their information. You also NEVER take but one program's information as fact. Always confirm it with another monitor.
In addition to that I've not seen my task manager wrong with respect to my CPU. It says my CPU is at 1.4GHz. It'll go down to 800MHz if my browser is closed. You can also see https://postimg.org/image/nwk4pfrn7/ that Windows shows my chip and its default speed. Both of which are correct.
You are possibly interpreting something wrong, using the wrong monitoring program or trolling.
What do you mean that it's usually wrong? I've checked Task Manager on all of my computers and they all show the exact speed that the CPU supports.
I don't know exactly how it gets the speed, but I'd imagine that it talks to the BIOS/UEFI for that info.
A CPU is similar to a car engine. Just because it has x amount of power (Ghz for CPUs and horsepower for engines), doesn't mean that it will always run at max power/speed. It's inefficient and of not real benefit unless an application needs that power.