An important new development was the advent of computers for the purpose of composing music, as opposed to manipulating or creating sounds. Iannis Xenakis began what is called musique stochastique, or stochastic music, which is a composing method that uses mathematical probability systems. Different probability algorithms were used to create a piece under a set of parameters. Xenakis created early tape pieces such as Concret PH (1958) without the use of stochastics, and experimented with spatialization and multimedia, creating polytopes such as the Polytope de Montréal. Xenakis used computers to compose pieces like ST/4 for string quartet and ST/48 for orchestra (both 1962), Morsima-Amorsima, ST/10, and Atrées. He developed the computer system UPIC for translating graphical images into musical results and composed Mycènes Alpha (1978) with it.