I am ignorant when it comes to where companies look when they are hiring, but your comment makes it seem like companies can choose sources that are somehow segr

I am ignorant when it comes to where companies look when they are hiring, but your comment makes it seem like companies can choose sources that are somehow segregated by race/gender/etc. What/where are these sources? Do you really think microsoft has any trouble finding people who want to work there? Where else should they look? In all my time being a straight white male, I've never listed my resume on a "whites only" job site.