I'm guessing you're talking about gaming capture/recording?
You want a dedicated, seperate HDD for recording/capturing video. Don't use it for anything other than the raw video captures.
You want as many cores as possible (4-6 or even 8) and relatively quick RAM (1600 or 1866 is plenty) for streaming.
And use good capture software. For newer intel CPUs with QuickSync, Myrillis Action is great for file size and CPU overhead. Fraps is also great and one of the most mature products for capture. MSI Afterburner is FREE and also very good, but I consistently get better FPS with FRAPS. Another option worth testing is DXtory, which is more complex but worth the effort if it works well for you.