The phonograph and radio had been invented in the late eighteen hundreds.

VOA: special.2009.02.08

Good question, so there is this little reading head kind of like in an old phonograph player that does move back and forth and in and out depending on the implementation.

好问题，这就像,老留声机里的小读头,它通过来回移动,来完成不同的操作。

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