Computer Memory

A computer can process nothing until the data to be worked on and the instructions describing what to do with it are held somewhere inside the machine. That holding place is the computer's memory, and every computer system needs it before any processing can begin.

The word "memory", when used on its own, almost always refers to the main or primary memory — the memory the processor works with directly while the computer is running. This is the computer's active workspace: programs and data sit here while they are being used.

Alongside it, every system also has secondary memory, commonly called a storage device. Its job is different: it keeps data, instructions and results permanently, so that they survive after the work is done and remain available for future use. Files you save, software you install and results you keep all live in secondary memory.

The distinction to carry forward is one of purpose:

• Primary (main) memory — the working memory the system talks about by default; holds what is currently being processed. …