Secondary memory

          Secondary memory is labeled as such because data stored within secondary storage media (usually disk drives) do not communicate directly with the microprocessor. Any data stored in such media is first transferred to a RAM device for processing to take place. This type of memory is also non-volatile and permanent since it permits long time storage as opposed to volatile memory. Secondary memory is subdivided into two categories:

• Internal devices are designed to be placed inside the computer at all times. Examples include:

Read-only memory (ROM)	Memory chips storing permanent data and instructions. Their data cannot be modified, hence the name read-only.
Flash memory	This type of memory can be erased electronically and rewritten. It helps to hold computer’s start-up instructions because it allows the computer to update its contents easily.
Complementary metal-oxide semiconductor (CMOS)	It provides high speed and consumes little power. CMOS technology uses battery power to retain information even when the power of computer is off.
Hard disk drives (HDD)	Secondary storage device that consists of one or more platters to which data is stored using magnetic particles. The entire device is enclosed in an airtight, sealed case to protect it from contamination.
Solid state disk (SSD) drives	Solid state drives stores the data in flash memory chip. There are no moving parts in flash memory, making it more durable and shock resistant, however, it is more expensive than other types of media.

 

• External devices are stand- alone devices that separated from computer. They are connected to the computer with a cable plugged into a suitable interface such as USB port. Examples include:

External hard disks	A hard drive (HDD) or solid-state drive (SSD) that is connected to a computer on the outside rather than on the inside.
Optical disks (DVD and CD)	A type of storage media that consists of a flat, round, portable metal disc made of metal, plastic and lacquer that is written and read by a laser.
USB flash drives	Portable flash memory storage device that plug in a USB port.
Solid state memory card	Removable flash memory, usually not bigger than 1.5 inches in height or width that inserted into built-in card slot or card reader/writer to transfer the stored items.