Some old PCs didn't have storage, so users needed to add programs manually by typing in the source code. As The 8-Bit Guy explains, one of the first consumer solutions was to attach a cassette tape to the computer through analog audio cables. They would actually be programmed by pulsing electrical intensities, which would be interpreted as binary data, within the audio range. Near the end, he even plays a clip of normal data, and “fast loader” data.
He, and his co-hosts, talk about their experiences with the medium, such as using a two-deck cassette player to copy programs and share them with friends. It doesn't go too deep into the technology or the time period, unlike some of his previous videos, but it's still entertaining none-the-less.