The term studio system refers to the practice of large motion picture studios
1. producing movies primarily on their own film making lots with creative personnel under often long-term contract and
2.  pursuing vertical integration through ownership or effective control of  distributors and movie theaters, guaranteeing additional sales of films  through manipulative booking techniques.
  The Little Three studios (Universal,  Columbia and  United Artists)  also made pictures, but each lacked one of  the crucial  elements of  vertical integration.The   Big Five tryed to achieve vertical integration through the late   1940s, owning vast real estate on which to construct elaborate sets. In   addition, these studios set the exact terms of films release dates and   patterns, and operated the best movie palaces in the nation. 
Warner Bros, Paramount, 20th Century Fox, Loew's (MGM) and RKO. Together these eight companies operated as a big monoploly controlling the entire market.
Warner Bros, Paramount, 20th Century Fox, Loew's (MGM) and RKO. Together these eight companies operated as a big monoploly controlling the entire market.
They   also controlled the terms under which you could see their films.   Prestige or A-level films used studio stars and lavish production   values, and then could only be seen initially in studio-owned, first-run   theaters. When the studios released these films to theaters they  didn't  own, they forced those owners to buy A-pictures in combination  with a  number of often awfull, B-movies (no stars,crappy genre   pictures) and shorts, a practice called "block booking." also, the   studios often made the exhibitors buy the films blind, not allowing them   to see what they were getting before they got it. 
  On May 4, 1948, in a federal antitrust suit known as the Paramount case   brought against the entire Big Five, the U.S. Supreme Court   specifically outlawed block booking. Holding that the conglomerates were  in violation of antitrust, the justices refrained from making a  final  decision as to how that fault should be remedied, but the case was  sent  back to the lower court from which it had come with language that   suggested divorcement which ment the complete separation of exhibition  interests  from producer-distributor operations—was the answer.
 Actors and actresses were contract players bound up in seven-year  contracts to a single studio  because the studio system also hinges on the treatment of stars, who   were made and exploited to suit a studio's image and schedule. The  studio generally held all the  options. Stars could be loaned out to  other production companies at any  time. Studios could also force bad  roles on actors, and control the  minutiae of stars' images with their  mammoth in-house publicity  departments.