CS 100 (Learn) — CS 100 (Web) — Module 02
We will describe secondary storage first because it is more tangible than primary memory and we can interact with it directly.
Secondary storage is the long term (permanent) storage of a computer. Secondary storage devices you are probably familiar with include hard drives, flash drives, CDs and DVDs. Historical devices include magnetic tapes and floppy disks.
For most of modern computing, the most common type of secondary storage devices have been hard drives. Inside of a hard drive there are several magnetic disks (or platters) that can store an incredible amount of information in a small amount of space. Hard drive capacities are measured in terabytes (TB) or trillions of bytes. Hard drives are called "drives" because there is a physical motor that spins the magnetic discs (just like you 'drive' a car when the engine spins the wheels around).
Flash drives are becoming increasingly popular as secondary storage devices. Although the technology behind flash drives is complicated, the core technology is more like static electricity than the magnetism used by hard drives. Flash drives include USB sticks and the SD cards made popular by digital cameras. There are also high speed and higher capacity flash drives known as Solid State Drives (SSDs). Because they have no moving parts, flash drives require significantly less power than hard drives, making them very popular in mobile devices. Modern SSDs are also faster than hard drives, but they have not completely replaced hard drives because (a) they currently have lower capacities and (b) they are more expensive. There is no reason to call a flash drive or SSD a "drive" because there is no motor or any moving parts, but the name has stuck to ease the transition for consumers.
The secondary storage of a computer typically contains:
Because the secondary storage stores everything you need, it begs the question what the primary memory is needed for.