The 'OtherOS' functionality was not present in the updated PS Slim models, and the feature was subsequently removed from previous versions of the PS3 as part of the machine's firmware update version 3.21 which was released on April 1, 2010; Sony cited security concerns as the rationale. The firmware update 3.21 was mandatory for access to the PlayStation Network. The removal caused some controversy; as the update removed officially advertised features from already sold products, and gave rise to several class action lawsuits aimed at making Sony return the feature or provide compensation.

What functionality did the PlayStation 3 lose in version 3.21 of its firmware update?