The characteristics of desktop memory: write RAM (read and write memory, memory bar) in the data will be completely disappeared after power off, the computer boot CPU first read into the execution of the program data from ROM (read-only memory). Memory is a computer (including SCM), the basic components, from the day there is a computer memory. And the external storage belongs to the computer peripheral equipment, the hard disk is after the development of magnetic tape, floppy disk after the production of external storage.