Together with a piece called Atlas Borealis with Ten Thunderclaps, Cage submitted the idea for HPSCHD, which had been commissioned by the Swiss harpsichord aficionado Antoinette Vischer.
The long and complex compositional process also involved the technical assistance of Jim Cuomo, Laetitia Snow, James Grant Stroud, and Max Mathews.
Conceived as a highly immersive multimedia experience, the performance featured David Tudor, Antoinette Vischer, William Brooks, Ronald Peters, Yūji Takahashi, Neely Bruce and Philip Corner playing harpsichords whose sounds were captured and amplified, 208 tapes playing computer-generated sounds through 52 monaural tape players, and an array of movie and slide projectors projecting 6400 slides and 40 movies onto rectangular screens, on a 340-foot circular screen, and on the domed ceiling of the Assembly Hall.
The harpsichord solos were created from randomly processed pieces by Mozart, Beethoven, Chopin, Schumann, Gottschalk, Busoni, Schoenberg, Cage and Hiller, rewritten using a FORTRAN computer program designed by Ed Kobrin based on the I Ching hexagrams.
These printouts, executed on a CDC 6400 computer at the State University of New York at Buffalo, in April 1969, offered a series of randomly generated settings for volume, treble and bass for each channel at intervals of 5 seconds.