The built-in memory of a computer typically refers to RAM (Random Access Memory). RAM is a type of volatile memory that the computer uses to temporarily store data that is actively being used or processed. It provides fast access to the data the computer needs to perform tasks, and its content is erased when the computer is powered off.

RAM (Random Access Memory) is an example of volatile memory. Volatile memory is a type of computer memory that requires power to maintain the stored information. When the computer is powered off or restarted, the data stored in RAM is erased. This is in contrast to non-volatile memory like hard drives or SSDs, where data is retained even when the power is turned off. Volatile memory, such as RAM, provides fast access to data for the computer's processor but does not retain data when the system is powered down.

Actually, the correct acronym for Reusable Optical Storage is not ROM. The correct acronym is ROS, which stands for Reusable Optical Storage. ROS refers to a technology that allows optical storage media, such as DVDs and CDs, to be rewritten or reused multiple times for data storage purposes.