Which type of memory can only be read and usually cannot be changed?

Read-only memory (ROM) is a type of non-volatile memory that is designed primarily for the purpose of storing firmware or software that is not meant to be modified frequently, if at all. This characteristic is crucial because it ensures that the system can boot and run essential programs, such as the BIOS in computers, without risk of accidental alterations. The data in ROM is typically written during the manufacturing process and can only be read by the system, hence the name "read-only."

In contrast, Random Access Memory (RAM) and Cache memory are types of volatile memory that play a role in temporarily holding data and programs that are actively in use, allowing for fast read and write operations. Flash memory, while able to retain information without power, is different because it is designed to be erased and rewritten, unlike ROM. Thus, while both RAM and Cache are important for system performance and speed, and Flash memory is useful for storage and portability, they do not fit the definition of memory that is primarily read-only with limited capability for modification.