Both factions of the Generation One Transformers had their own mini-cassette units: smaller robots that were closer to humans in size. They are capable of transforming into audio cassettes, shrinking down as they change shape so that they may interface with any Earth cassette-playing device. The Decepticons had a larger group of cassettes than the Autobots and often used them to infiltrate and spy on human government establishments or scientific facilities, whereas the Autobot cassettes were only ever deployed in battle or recon missions.
There are only four Autobot cassettes. Their guardian is Blaster.
The Decepticon cassettes are frequently deployed in combat and infiltration missions. They are commanded by Soundwave.