Spotify's own engineers measured one week of the desktop app, 23-29 March 2010: 8.8 % of the music came from Spotify's servers, 35.8 % from other listeners' computers, and 55.4 % from the listener's own drive.

Every laptop kept the songs it played. By default it set aside up to a tenth of the free disk space, at most 10 GB (about 2,000 songs at 5 MB each), encrypted, and when it filled up, the song played longest ago went first. That same store was what it lent to strangers: only whole songs, to at most four other listeners at a time, and it stopped sending whenever its own music had less than 3 seconds left in memory. A song you had never played started with about 15 seconds from Spotify's server while the laptop looked for listeners who had the whole song.

Phones never took part: "The smartphone clients do not participate at all in the peer-to-peer protocol." In 2014 Spotify told TorrentFreak it was "gradually phasing out" the desktop sharing. The cache stayed: Spotify still keeps parts of songs on your device "so it can play without lagging", and you can clear it under Settings, Storage.

The laptops, the server and the songs are our own simplified drawings.

Did you know your laptop used to send music to strangers?

Sources: Kreitz and Niemelä (KTH and Spotify), "Spotify: Large Scale, Low Latency, P2P Music-on-Demand Streaming", IEEE P2P 2010; Kreitz, "Spotify: Behind the Scenes", KTH 2011; TorrentFreak, 16 April 2014; Spotify Support, storage information (read October 2026).
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