A good way to determine a baseline knowledge set for hardware knowledge generally needed for Comp Sci studies is to visit the curriculum websites of a wide range of prestigious universities. For me, I'd check the Comp Sci curriculum at MIT, Stanford, University of Illinois at Urbana/Champaign (UIUC), Georgia Tech, etc. Then I'd get an average understanding from that.
Furthermore, you could also personally phone up guidance counselors at Universities to which you are either attending or applying in order to get a personalized view of your needs. They would be available to guide you based on your desires. Professors even more. They are surprisingly accessible and very willing to give feedback on things like this.
Recently, I looked at grabbing my master's degree. As an alum of UIUC, I emailed a few old professors there and told them of my interest. I asked them several questions geared at understanding gradschool and their perspective. They shared and most invited me to call and chat.
Personally, I'd agree with @CookieOfFortune. The more you know about how a computer works internally, the more you can use that to your advantage while writing software. That said, it's not as if you really need to understand the physics of electronics to a high degree. It's interesting, sure, but your focus should be on circuitry, logic, etc. Much of this should be presented in a good Operating Systems course or at least provide you with springboards to learn more on your own.