The Zero System is a machine installed in some Gundams later in the GW series. It gives you unbelievable battle skills but is very harmful to the brain. It basically makes you lose your conscience and the computer takes over your brain. All targets are located in your brain and your uncontrollable. You will end up destroying things you don't need to. No one other than Heero ever get close to conquering the Zero System if any of them really do. Heero "conquers" it at the end of the series. Wing Zero and Epyon are the only Gundams to keep the Zero System but the others were at one time equipped with it, and some never even used it.