The first three tracks are serene, gentle tape-looped guitar textures performed by Robert Fripp and accented with treatments, synthesizer and piano by Brian Eno.
Track four, "Wind on Wind", is an excerpt from Eno’s solo project Discreet Music, which was released after this album. Eno had originally intended Fripp to use the material which became Discreet Music as a backing tape to play over in improvised live performances.
The second half of the album is a groundbreaking twenty-eight minute piece of drone music titled "An Index of Metals", in which guitar notes are accumulated in a loop, with distortion increasing as the track progresses.
Tracks from this album were used for the music on the The Hitchhiker's Guide to the Galaxy Primary Phase.