Is mining using with cpu(some web sites) fake or not There is a rule about every browser :
Browser can not access client's RAM-CPU-HARD DRIVE-WEB CAMERA-And other resources of client's machine.
Am i right?
So how some web sites do mining using client's cpu?
Are they scam or they are real?
There are two things mining requires in general:


Processing power (CPU/GPU)
RAM


For Bitcoin, a tiny RAM is OK, but for Ethereum, a few GBs of RAM is needed.


  So how some web sites do mining using client's cpu?


Using Javascript (unfortunately. There are more efficient ways, such as TurboJS or GPUJS or WebAssembly). Basically, they're trying xs with different nonce fields until Hash(x) is smaller than a target value.

Bitcoin mining is possible wherever there's general-purpose processing power. Is it feasible? No. Because of ASIC miners, CPU or even GPU mining have higher electricity costs compared to mining revenue.

On the other hand, it might be different for other coins, such as Monero. You might have heard of CoinHive, which had Proof-Of-Work captchas that required mining Monero for a few seconds. Because Monero is ASIC-resistant, CPU mining used to be efficient. (Until February 2019, when CoinHive miner was discontinued due to the falling value of Monero).

It's likely that they might be scam, otherwise it's unprofitable for you (assuming you pay for electricity).