Which memory type is read-only and is primarily used for firmware?

The correct answer is based on the defining characteristics of read-only memory (ROM). ROM is non-volatile memory that retains its information even when the power is turned off, which is crucial for storing firmware—the permanent software programmed into the hardware. Firmware is responsible for low-level control of a device's hardware, and it must be reliable and readable without modification, which is why it is stored in ROM.

Unlike RAM, which is volatile and used for temporary data storage while a computer is running, or cache memory, which serves as a high-speed access layer between the CPU and the RAM, ROM is designed explicitly for long-term storage of critical system instructions. Additionally, hard drive memory is a larger, more flexible storage option that can be written to and erased multiple times, making it unsuitable for the specific, stable storage needs of firmware applications.

This distinction highlights the specialized purpose of ROM in computer architecture, making it the correct choice for the question about memory types that are read-only and primarily used for firmware.