Composers such as Pierre Schaeffer in the 40s and Edgar Varese in the 50s realised that with this technology they didn´t need to write music for humans to play at all: they could compose for the tape player or a mixture of tape, vinyl and live musicians.
Schaeffer coined the term Musique Concerte for this new kind of music that manipulated real sounds in different ways. He also invented loops and the first sampling machine with which he wrote a piece using sampled locomotive sounds.
You can read more about music concerte and
And there is a brief biography of Edgar Varčse here: w3.rz-berlin.mpg.de/cmp/varese.html