Many early microcomputers (including the MITS Altair) used standard audio cassettes for persistent storage. The CUTS and Kansas City standards were common inte

Many early microcomputers (including the MITS Altair) used standard audio cassettes for persistent storage. The CUTS and Kansas City standards were common interchange formats for cassette data, far cheaper than punched paper tape or magnetic tape reels. The computer/cassette interface converted binary data to and from audio tones, which were then written and read via the microphone and headphone interfaces (usually 3.5" jacks) on a cassette recorder. Sending this audio over free air would have resulted in "wireless data transfer" ... See: https://en.wikipedia.org/wiki/Kansas_City_standard https://en.wikipedia.org/wiki/Kansas_City_standard