I have a SB2 13" gtx 1050 and i7 8650u @ 1.90GHz. So newbie question here how do I increase the cpu frequency to 4.20GHz or at least something higher than 1.90GHz it seems to always be on 1.90GHz.
You can't overclock the SB2. Trying to do so would be a great way to fry it, since there is no active cooling on the SB2 13 inch model. You would quite literally be burning money.
These SoCs are dynamic and can burst higher, what are you wanting to accomplish with a 4.2GHz on a mobile device? Is there something where the CPU is causing a bottleneck?
