RCA introduced its Sound Tape cartridge, a magnetic tape audio format, in 1958. Sound Tapes were designed to be more convenient than open reel as they avoided the need to thread tape into the machine.
Like open reel it used quarter inch tape but ran at 3.75ips (the slower speed that was available on open reel machine), and like the later Compact Cassette the cartridge was reversible (some players even had auto-reverse mechanisms). There are four tracks on the tape, two interleaved stereo pairs, and a typical play time of 30 minutes per side.
Sound Tapes are around three times the size of a Compact Cassette.
The format was not a success, as players were slow to appear, and RCA were slow to license pre-recorded music. It had disappeared from shops by 1964.