The Hollow Bastion OS was the operating system installed by Ansem the Wise to be used in Hollow Bastion. It was modified from a copy of a system created by the ENCOM corporation, and is the setting for the world Space Paranoids. It represents Tron's world in Kingdom Hearts II. The system was originally seen in Disney's groundbreaking movie Tron.

The system was originally used by Ansem the Wise, but when he was exiled by his apprentices, Xehanort restored the Master Control Program and Sark. The dataspace, where all the systems original data was stored, was named the DTD, after the Door to Darkness, and could be accessed by a password that was the names of the seven Princesses of Heart.

Sora and his friends traveled there and met Tron, who had been imprisoned for trying to take on the MCP. They eventually succeeded in doing so, after Cid and Merlin created an extermination program. In gratitude, Tron, now the system administrator, showed the Hollow Bastion residents the town's true form, that of Radiant Garden.