Principal Types Of Secondary Storage Devices

Published Date: 02 Nov 2017

Alternatively referred to as external memory and auxiliary storage, secondary storage is a storage medium that holds information until it is deleted or overwritten. Secondary storage devices, as indicated by the name, save data after it has been saved by the primary storage device, usually referred to as RAM (Random Access Memory). From the moment of starting typing a letter in Microsoft Word, for example, and until it is saved, the entire work is stored in RAM. However, once the machine is powered off, that work is completely erased, and the only copy remaining is on the secondary storage device where it was saved, such as internal or external hard disk drive, optical drives for CDs or DVDs, or USB flash drive.

There are several types of secondary storage devices used today. These devices can be compared to each other in terms of portability, speed and capacity.

Magnetic Tape is a recording medium consisting of a thin tape with a coating of a fine magnetic material, used for recording analogue or digital data. A device that stores computer data on magnetic tape is a tape drive. The capacity of tape media are generally on the same order as hard disk drives. Magnetic Tapes Generally transfer data a bit slower than hard drives, however magnetic tapes are cheaper and more durable.

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Floppy Disks were a ubiquitous form of data storage between 1980's and early 2000's, However they have now been superseded by data storage methods with much greater capacity, such as USB flash drives.

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A hard disk drive (HDD) is a data storage device used for storing and retrieving digital information using rapidly rotating discs (platters) coated with magnetic material. An HDD retains its data even when powered off. An HDD consists of one or more rigid ("hard") rapidly rotating discs (platters) with magnetic heads arranged on a moving actuator arm to read and write data to the surfaces.

The hard disk drive is the main and usually largest data storage device in a computer. It is a non-volatile, random access digital magnetic data storage device. A hard drive is made up of platters which store the data, and read/write heads to transfer data. A Hard Drive is generally the fastest of the secondary storage devices, and has the largest data storage capacity. Hard drives however, are not very portable and are primarily used internally in a computer system. Some persons use hard drives externally as a form of storage and as a substitute for portable storage. Hard drives used for these purposes are called external hard drives. A Hard Disk is divided into tracks and sectors. Data on hard disk is positioned into these tracks and sectors so they can be easily read by the heads and also to help reduce fragmentation on the hard disk.

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Below are 2 diagrams depicting how a hard disk is divided into tracks and sectors:

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The two most common form factors for modern HDDs are 3.5-inch in desktop computers and 2.5-inch in laptops. HDDs are connected to systems by standard interface cables such as SATA (Serial ATA), USB or SAS (Serial attached SCSI) cables.

As of 2012, the primary competing technology for secondary storage is flash memory in the form of solid-state drives (SSDs). HDDs are expected to remain the dominant medium for secondary storage due to predicted continuing advantages in recording capacity and price per unit of storage, but solid state drives are replacing rotating hard drives especially in portable electronics where physical size and durability are more important considerations than price and capacity.

Optical disk is an electronic data storage medium from which data is read and written to by using a low-powered laser beam. It is flat, circular, plastic or glass disk on which data is stored in the form of light and dark pits. There are three basic types of optical disks: Read-only optical disks, Write once read many Optical disks and Rewritable Optical disks. Two main types of optical disks are:

CD - is an abbreviation of Compact Disk, and is a form of data storage that can transfer data up to the speed of 7800 KB/s. A standard 120 mm CD holds up to 700 MB of data, or about 70 minutes of audio. There are two types of CD: CD-ROM and CD-RW. CD-ROM stands for CD-Read Only Memory and they function the same way Read Only Memory does. CD-RW stands for CD-Rewritable. These disks can be erased and rewritten at any time.

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DVD: is an abbreviation of Digital Versatile Disc, and is an optical disc storage media format that can be used for data storage. The DVD supports disks with capacities of 4.7 GB to 17 GB and access rates of 600 KBps to 1.3 MBps. A standard DVD disc store up to 4.7 GB of data. There are two types of DVD's: DVD-ROM and DVD-RW. DVD-ROM stands for DVD-Read Only Memory and they function the same way Read Only Memory does. DVD-RW stands for DVD-Rewritable. These disks can be erased and rewritten at any time.http://www.clker.com/cliparts/9/c/0/a/1195422643201049780Machovka_DVD.svg.med.png

A flash drive is a small external storage device, typically the size of a human thumb that consists of flash memory.USB flash drives are removable and rewritable reads and writes to flash memory. They are a solid-state storage medium that's both inexpensive and durable. Currently, USB 2.0 flash drives on the market are able to reach a data transfer speed of 480 Mbit/s and USB 3.0 has transmission speeds of up to 5 Gbit/s. USB Flash drives vary in sizes from 8 Megabytes to 512 Gigabytes. More commonly used sizes vary from 2 Gigabytes -32 Gigabytes.

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A memory card or flash card is an electronic flash memory data storage device used for storing digital information. They are commonly used in many electronic devices, including digital cameras, mobile phones, laptop computers, MP3 players and video game consoles. They are small, re-recordable, and able to retain data without power.

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