The correct answer is A. Semiconductor memory.
Semiconductor memory is a type of computer memory that uses semiconductor devices to store and retrieve data. It is the most common type of memory used in computers today. Semiconductor memory is volatile, meaning that it loses its contents when power is turned off.
Magnetic disks are a type of secondary storage that uses magnetic fields to store data. They are typically made of metal or plastic and have a thin layer of magnetic material on their surface. Data is stored on magnetic disks in the form of tiny magnetized spots.
Magnetic drums are a type of secondary storage that uses a rotating drum to store data. The drum is coated with a magnetic material, and data is stored on the drum in the form of tiny magnetized spots.
Magnetic tapes are a type of secondary storage that uses magnetic tape to store data. The tape is coated with a magnetic material, and data is stored on the tape in the form of tiny magnetized spots.
Semiconductor memory is not used as secondary storage because it is volatile. This means that it loses its contents when power is turned off. Secondary storage is used to store data that needs to be accessed even when the computer is turned off.