These are also frequently attached externally through a Universal Serial Bus (USB), and they also used in redundant and recoverable storage networks in case of accidental loss of data. All modern computers usually use at least one internal hard disk drive (HDD). Magnetic or hard drives are the most common type of secondary memory. Unlike primary memory, secondary memory also does not access the CPU directly from the computer. Primary memory (RAM) is faster but does not store data permanently, instead of loading secondary memory slower data in the primary memory to make efficient use of it. Secondary memory is cheaper than primary memory but is also slower in both reading and writing. Secondary memory devices are nonvolatile in nature and data does not disappear when the computer turned off and on again. Secondary memory devices are not only convenient for storing backup files, but they also allow computer users to expand their ability to transfer large amounts of data to another Secondary memory devices. Primary storage devices are known as Random access memory (RAM), While RAM (Random Access Memory) has fewer data storage capacity, and the data got disappeared when the computer is turned off. The processed data is, generally, stored in a digital format either on a hard disk drive (HDD) or floppy disk drives, optical drives, tape drives, external hard drives, RAID and USB storage devices, which is called Secondary memory, or removable mass storage devices(MSDs). It is slower than RAM but larger storage capacities than primary memory. The Secondary memory store data that can be easily retrieved only by the main memory and used by the processor. It’s content firstly copied into ram and then transferred to CPU. It is characterized by its slowness and cheapness, relative to the RAM, and by its permanent appearance. This memory is also called permanent, external, stable or persistent memory. The secondary memory is accessed indirectly via input/output operations. Secondary memory is also known as secondary storage.