slotRadio was a proprietary format developed by SanDisk that delivered music on a microSD memory card.
[1] Songs could only be played using a SanDisk Sansa music player that supported the SlotRadio formatted microSD cards.
[3] SlotRadio gave consumers access to a large library of music but unlike individual MP3s that were purchased, the playlist was predetermined and the user had only the ability to skip songs forward, much like a radio or music streaming service Pandora, hence the name slot "Radio".
Cards could be purchased in different musical genres such as rock, country, oldies and hip hop/R&B.
Each card contains several playlists by "mood" or environment such as workout, while featuring songs from Billboard's top charting artists.