Secondary storage is a type of memory that can hold data for long periods of time, even when there is no power to the computer. Programs are normally stored in secondary memory and loaded into main memory as needed. Important data, such as word processing documents, payroll data, and inventory records, is saved to secondary storage as well.
The most common type of secondary storage device is the disk drive. A traditional disk drive stores data by magnetically encoding it onto a spinning circular disk. Solid-state drives, which store data in solid-state memory, are increasingly becoming popular. A solidstate drive has no moving parts and operates faster than a traditional disk drive. Most computers have some sort of secondary storage device, either a traditional disk drive or a solid-state drive, mounted inside their case. External storage devices, which connect to one of the computer’s communication ports, are also available. External storage devices can be used to create backup copies of important data or to move data to another computer.
In addition to external storage devices, many types of devices have been created for copying data and for moving it to other computers. For many years floppy disk drives were popular. A floppy disk drive records data onto a small floppy disk, which can be removed from the drive. Floppy disks have many disadvantages, however. They hold only a small amount of data, are slow to access data, and can be unreliable. Floppy disk drives are rarely used today, in favor of superior devices such as USB drives. USB drives are small devices that plug into the computer’s USB (universal serial bus) port and appear to the system as a disk drive. These drives do not actually contain a disk, however. They store data in a special type of memory known as flash memory. USB drives, which are also known as memory sticks and flash drives, are inexpensive, reliable, and small enough to be carried in your pocket.
Optical devices such as the CD (compact disc) and the DVD (digital versatile disc) are also popular for data storage. Data is not recorded magnetically on an optical disc, but is encoded as a series of pits on the disc surface. CD and DVD drives use a laser to detect the pits and thus read the encoded data. Optical discs hold large amounts of data, and because recordable CD and DVD drives are now commonplace, they are good mediums for creating backup copies of data.
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