The correct answer is option 'D': Tertiary.

Tertiary storage refers to a system where a robotic arm connects or disconnects offline mass storage media according to the computer operating system demands. Let's understand this concept in detail:

Tertiary Storage:
Tertiary storage is a type of storage system that sits between secondary storage (such as hard drives) and offline storage (such as tapes or optical discs). It is designed to provide long-term, low-cost storage for large amounts of data that is not frequently accessed. Tertiary storage is typically used for backup and archiving purposes.

Robotic Arm:
A robotic arm is a mechanical device that is capable of performing tasks with a high degree of accuracy and precision. In the context of tertiary storage, a robotic arm is used to connect or disconnect offline mass storage media, such as tapes or optical discs, to the computer system.

Connection and Disconnection:
The robotic arm in a tertiary storage system is responsible for connecting or disconnecting the offline storage media as per the demands of the computer operating system. When the computer system requires access to a specific file or data stored on the offline media, the robotic arm connects the appropriate storage media to the system. Once the data transfer is complete, the robotic arm disconnects the media and returns it to its original position.

Computer Operating System Demands:
The computer operating system manages the storage hierarchy and determines when data should be retrieved from tertiary storage. It sends commands to the robotic arm to connect or disconnect the appropriate offline storage media based on the data access requirements.

Advantages and Limitations:
Tertiary storage offers several advantages, including large capacity, low cost per unit of storage, and long-term data retention. However, it also has limitations such as slower access times compared to primary and secondary storage and the need for a robotic arm to handle the offline media.

In conclusion, tertiary storage is a storage system where a robotic arm connects or disconnects offline mass storage media based on the demands of the computer operating system. This allows for efficient and automated access to large amounts of data stored on tapes or optical discs.