<P> An exception to this standard were mechanical storytelling dolls from the 1980s (e.g. Teddy Ruxpin) which used the Type IV metal configuration cassette shell but had normal Type I voice grade tape inside . These toys used the Type IV notches to detect that a specially coded tape had been inserted, where the audio of the story is stored on the left channel and various cue tones to tell the doll's servos how and when to move along with the story on the right channel . </P> <P> Most pre-recorded chrome cassettes require 120 μs equalisation and are treated as Type I (with notches as Type I ferric cassettes), to ensure compatibility with budget equipment . </P> <P> Tape length usually is measured in minutes of total playing time . The most popular varieties are C46 (23 minutes per side), C60 (30 minutes per side), C90, and C120 . The C46 and C60 lengths typically are 15 to 16 micrometers (0.59 to 0.63 mils) thick, but C90s are 10 to 11 μm (0.39 to 0.43 mils) and (the less common) C120s are just 9 μm (0.35 mils) thick, rendering them more susceptible to stretching or breakage . BASF declared the C60 with 88 meters (289 feet). Some vendors are more generous than others, providing 132 or 135 meters (433 or 443 feet) rather than 129 meters (423 feet) of tape for a C90 cassette . Even C180 tapes were available at one time, but these were extremely thin and fragile and suffered from such effects as print - through, which made them unsuitable for general use . 150 minute length is still available from Maxell (UR 150), Sony (CDixI 150) and TDK (TDK AE 150). </P> <P> Although the TDK - D C180 was produced for a decade (1972--82), it is very rare, because of several technical flaws . The tape had to be so thin that it was nearly transparent and therefore had fewer particles to magnetize, resulting in a poor sound quality and even worse durability . It required a strong motor to be driven, and had high wow - and - flutter . Finally, it took a relatively long time to rewind . </P>

How long can you record on a cassette tape
find me the text answering this question