[wjnc]

Cassette tapes doubled as music storage and data storage for machines like ZX Spectrum and C64. You could just copy software like you would copy a music cassette. Code via radio would be as easy as playing a song. Another time long gone computer magazines would print code that you could enter yourself! Before that Sussman is reported to meditate on code, and acolytes where supposed to create machines that could run that code.

[dhosek]

Pretty much all the early 8-bit computers had cassette storage. On the Apple ][ series, the interface to write to the cassette was identical to the speaker interface so you could load audio into memory from a cassette and play it back (at 1-bit resolution) on the internal speaker of the Apple ][. It sounded like crap (although a lot of cassette decks did too) but seemed like magic.

[shrx]

Here are some details about the ZX Spectrum tape interface:

http://www.zxdesign.info/cassette.shtml

https://sinclair.wiki.zxnet.co.uk/wiki/Spectrum_tape_interfa...