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Auxiliary memory, also known as auxiliary storage, secondary storage, secondary memory or external memory, is used to store a large amount of data at lesser cost per byte than primary memory. They are two orders of magnitude less expensive than primary storage. In addition, secondary storage does not lose the data when the device is powered down—it is non-volatile. Another difference from primary storage in that it is not directly accessible by the CPU, they are accessed via the input/output channels. The most common form of auxiliary memory devices used in consumer systems is flash memory, optical discs, and magnetic disks. The latest addition to the auxiliary memory family is flash memory. This form is much faster as compared to predecessors, as this form of auxiliary memory does not involve any moving parts . In some laptops, such as Apple's MacBook Air line and MacBook Pro with Retina Display line, solid state drives (SSDs) made from flash memory have replaced magnetic disk based hard disk drives (HDDs) that are found in most laptops. These 'chips' of memory are found below the trackpad in those laptops. However, it is much more expensive to get large capacity flash storage chips as opposed to HDDs, many of which are inexpensive. In addition, it is difficult for average users to replace these chips.
Forms of Auxiliary Memory
- Flash memory: An electronic non-volatile computer storage device that can be electrically erased and reprogrammed, and works without any moving parts. Examples of this are flash drives and solid state drives A version of this is implemented in many Apple notebooks.
- Optical disc: Its a storage medium from which data is read and to which it is written by lasers. Optical disks can store much more data—up to 6 gigabytes (6 billion bytes)—than most portable magnetic media, such as floppies. There are three basic types of optical disks: CD-ROM (read-only), WORM (write-once read-many) & EO (erasable optical disks).
- Magnetic Disk: A magnetic disk is a circular plate constructed of metal or plastic coated with magnetized material. Both sides of the disk are used and several disks may be stacked on one spindle with read/write heads available on each surface. Bits are stored in magnetized surface in spots along concentric circles called tracks. Tracks are commonly divided into sections called sectors. Disk that are permanently attached and cannot removed by occasional user are called hard disks. A disk drive with removable disks is called a floppy disk drive.
- Magnetic tapes: A magnetic tape transport consists of electric, mechanical and electronic components to provide the parts and control mechanism for a magnetic tape unit. The tape itself is a strip of plastic coated with a magnetic recording medium. Bits are recorded as magnetic spots on tape along several tracks. Seven or Nine bits are recorded to form a character together with a parity bit R/W heads are mounted in each track so that data can be recorded and read as a sequence of characters.