If I may offer a small ATC insight to those who know little or nothing about ATC systems, and are fixated by concepts of Primary and Secondary radar, please have a look at the following link. This might give an insight into what actually goes on. The Civil ATC world does NOT run on radar: it runs on filed Flight Plans updated by radio communications, with radar providing supplementary information for conflict resolution or sequencing in the Terminal environment.
(Aircrew and ATC professionals are generally excused from reading the link
)
Flight progress strip - Wikipedia, the free encyclopedia