there are basically 2 types of superchargers centrifugal and postive displacement (and under positive displacement there are 2 types.)
centrifugal's are the ones that look kinda like snail shells and sit in the left or right of the engine. (Paxton, Vortech, Ati etc.)
Then there are the positive diplacements that basically sit on top of your engine and replaces the intake manifold. two models there, the Roots (03 Cobra, Saleen) and the twin screw. (Kenne Bell)
centrifugals tend to make the majority of their hp high in the powerband the positive displacement lower, the faster you spin the engine the more hp the centrifugals make. (depending on pully size and boost of course)
as far as roots vs twin screw the twin screw will make more hp while running same boost because of its better design, the twin screw is more efficient and doesnt run and discharge as hot.
those are just the bare basics but you can read a great article here
http://www.superchargersonline.com and learn alot. (look towards the bottom right hand corner for Superchargers A-Z)
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1995 Mustang GT 5.0
BBK CAI, Pro-M 75mm MAF, Pro-M Optimizer, BBK 70mm TB, GT-40 Intake, 24# Injectors, AFR 165's, 1.7 Roller rockers, Crane 2040 cam (E-303) BBK Equal Length headers, BBK O/R X-pipe, Flowmaster American Thunder 2 Chambers. FMS 3.73 Gears, Lentech AODE 2800 stall, BBK 255lph Fuel Pump, BBK Fuel Pressure Regulator. MSD 6AL, Steeda UDP's, FMS Aluminum drive shaft, Autologic chip Larocca tune.