Music to let your motor roll along by

In parallel with the development of the Compact Cassette, separate developments had been occurring in the USA, led by entrepreneurs Earl Muntz and Bill Lear, the latter of whom ran the airline Lear Jet. Whereas Muntz was primarily concerned with finding a way to easily playback jingles and adverts for radio (for which a version of his cartridge became the industry standard), Lear saw the potential to extend the format to the market for "music on the move".

8-Track Cartridges differ from cassettes in that they use what is termed 'co-axial' spooling - the take-up and supply spools are mounted on top of each other on the same axle. In effect, they are a single reel.

The tape is pulled out of the centre of the reel, wound around to the top of the cartridge where access holes allow contact by the playback head and capstan (through which the player's motor drives the tape forward). The tape that has pulled past the access holes is pulled back onto the outer side of the reel by the tension created by pulling on the inner side.

The simple mechanism that this enabled the players to use suited themselves to mobile applications where simplicity and cheap manufacture were the main aims, such as for aircraft and automobile music systems. They also found niche uses for 'mood music' (or 'Muzak') in supermarkets and even in lifts. Even arcade games of the 1970s (especially the mechanically driven type, like duck shoots and mole bashers) tended to use 8-Track cartridges for sound effects, as it was easy to switch and mix background music with vocal 'stabs' and other effects like explosions, shots and congratulatory fanfares.

The 8 available tracks were used to provide 4 stereo 'programmes' - a bit like sides on a cassette. However, all the Left channels were stacked together on one half of the tape's width, and all the Right channels on the other. The narrow track width tends in many circumstances to cause leakage between adjacent tracks, meaning you get to hear faint 'bleed-through' of one programme onto another - very often noticable in the gaps between songs. However cartridges in good condition played on well-aligned machines don't suffer from this to a degree sufficient to cause annoyance. The ends of the tape loop are joined by a short piece of foil strip, which is used by players to determine when to switch programmes.

It is perhaps no surprise that, as with cassette, EMI plumped for its big sellers on the new format in 1968. From mid-1968 to mid-1970, EMI 8-track cartridges looked rather like this copy of Sgt. Pepper.

The cartridge was decorated with a copy of the album cover on the top label, with another label on the underside showing the tracklisting and other credits and corporate information such as label logos, catalogue numbers, etc.