But isnt there a non-compete agreement with a lot of the engineers, at least higher level ones, that prohibit working for another company for a period of time after leaving a company, or are those illegal now?
Yes, but in states like CA, they are usually never enforced. If you make a living designing processors for a living, one company can't stop you from making a living in your field. On the other hand, they can still take you to court over it to try to ruin you at your new job and drain you financially.