Memory as part of a computer system

Memory is the computer's working space. Understanding the memory hierarchy — registers, cache, RAM, storage — explains most performance behaviour.

• RAM holds running programs and their data; it is volatile (cleared at power-off).
• More RAM lets more programs run without swapping to disk.
• Virtual memory: the OS uses disk space as overflow "RAM" — it works, but slowly.
• ROM holds permanent startup firmware.
• Hierarchy trade-off: the faster the memory, the smaller and more expensive it is.

• Volatile — loses contents without power (RAM); non-volatile keeps them (ROM, SSD).
• Virtual memory/paging — using storage to extend RAM.