Main memory, also known as RAM (Random Access Memory), is a crucial component of a computer that temporarily stores data and instructions that the CPU needs while performing tasks. It allows for quick read and write access, enabling efficient processing and multitasking. When a computer is powered on, the operating system and active applications are loaded into main memory for fast access. Unlike hard drives or solid-state drives, which provide long-term storage, main memory is volatile, meaning it loses its data when the power is turned off.