In this video, we get a close look at the construction and design considerations of an Edwards GXS screw pump with a Roots Booster. While watching this video, I am reminded that vacuum technology is a multi-disciplinary activity. These pumps are the result of mechanical engineers, electrical engineers and vacuum scientists.
I hope this video is helpful.
You can find the basics of roughing pump technology in Understanding Modern Vacuum Technology. Just click on the link in the right banner which will take you to Amazon.com.