Page "Muzak Holdings" Paragraph 31

Tape and player quality developments such as chrome tape and noise reduction allowed the cartridges and tape speeds to shrink, first to the size of an 8-track with eight monaural programs on a tape running at 1-7 / 8 IPS, to the size of a modern laptop hard drive and a speed of 15 / 16 IPS used by the Library of Congress for Talking Books.

As a result, before they were replaced with cassettes, the last of the tape cartridges were capable of carrying the same 8-1 / 2 hours per tape as the original 19-inch reels could carry per track.