Secondary Memory/ Storage Devices
Secondary memory, also known as Secondary storage or Auxiliary Memory, is slower and cheaper form of memory. It is a permanent storage device.
CPU does not access the secondary memory directly. The content in it must first be copied into the RAM to be processed. Secondary memory is non-volatile in nature. i.e. the information does not get erased even when power is switched OFF and data will not be destructed until and unless the user erases it.
Secondary Memory devices include:
Secondary memory, also known as Secondary storage or Auxiliary Memory, is slower and cheaper form of memory. It is a permanent storage device.
CPU does not access the secondary memory directly. The content in it must first be copied into the RAM to be processed. Secondary memory is non-volatile in nature. i.e. the information does not get erased even when power is switched OFF and data will not be destructed until and unless the user erases it.
Secondary Memory devices include:
- Magnetic disks- Floppy Disk, Hard Disk Drive, Magnetic Tape.
- Optical discs- CD(Compact Disk), DVD(Digital Video Disk), Blue-ray Disc.
- Solid State- Pen/Flash Drive, SSD(Solid State Drive).
(i) Floppy Disk (Diskette)
A Floppy Disk Drive (FDD) is a computer disk drive that enables a user to save data in removable diskettes. This portable storage device is a re-writable media and can be reused a number of times. It is round in shape and is covered by square plastic jacket.
Floppy disks are commonly used to move files between different computers. Although 8" disk drives made available in 1971 were the first real disk drives, the first widely used floppy disk were the 4", today these drives are being replaced with DVD, HDD and other writable disc drives and flash drives.
(ii) Hard Disk Drive
A Hard Disk Drive (HDD) is a non-volatile, random access digital data storage device. It is a data storage device used for storing and retrieving digital information using rotating disks (Platters) coated with magnetic material. All programs of a computer are installed in hard disk within a particular drive.
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| Hard Disk Drive |
It consists of a spindle that hold non-magnetic flat circular disks, called platters, which hold the recorded data. Each platter requires two read/write heads, that is used to write and read the information from a platter. All the read/write heads are attached to a single access arm so that they cannot move independently.
The information is recorded in bands, each band of information is called a track. Each Platter has the same number of tracks and a track location that cuts across all platters is called a cylinder. The tracks are divided into pie-shaped sections known as sectors.
(iii) Magnetic Tape
It is a medium of data storage, made up of a magnetic material. It is a storage medium on a large open reel or in a smaller cartridge or cassette (like a music cassette). It is used for those applications that are based on sequential data access medium.
(iv) Compact Disk (CD)
CD is an optical media that is used to store digital data, the compact discs are relatively cheap storage devices.
Compact disc (CD) are categorized into three main types:
- CD-ROM (Compact Disk-Read Only Memory) : Data is recorded permanently on the surface of the optical disk through the use of laser. The recorded content cannot be changed or erased by users. It is also called WORM (Write Once Read Many) disc. It is capable of storing large amounts of data-up to 1 GB, although the most common storage capacity is 700 MB.
- CD-R (Computer Disc Record able) : Data can be written on these discs only once. The data once stored in these discs cannot be erased.
- CD-RW (Compact Disc- Re-writable) : It is an erasable disc. CD-RW is used to write data multiple times on a disc by the use of format feature.
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| DVD |
Digital Video Disc (DVD) is also known as Super Density (SD) Disc. A DVD is an optical disc storage media manufactured for the first time by Philips, Sony, Toshiba and Panasonic in 1995. DVDs offer higher storage capacity than compact discs while having the same dimensions.
Depending upon the disk type, DVD can store several Gigabytes of data (4.7 GB-17.08 GB). DVDs are primarily used to store music or movies and can be played back on your television or on the computer too. They are not re-writable media.
DVDs come in three varieties:
- DVD ROM (Digital Video Disc-Read only Memory)
- DVD-R (DVD-Recordable)
- DVD-RW (DVD-Re-writable)
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| Blu-ray Disc |
(vi) Blu-ray Disc
Blu-ray disc (official abbreviation BD) is an optical disc storage medium designed to recapture the data normally in DVD format. Blu-ray Discs contain 25 GB (23.3 GB) per layer space. The name Blu-ray disc refers to the blue laser used to read the disc, which allows information to be stored at a greater density.
Blu-ray can hold almost 5 times more data than a single layer DVD.
The variations in the formats are as follows:
- BD-ROM (Read Only) for pre-recorded content
- BD-R (Recordable) for PC data storage
- BD-RW (Re-writable) for PC data storage
- BD-RE (Re-writable) for HDTV recording
A Flash drive is a data storage device hat consists of flash memory (USB memory/key memory) with an integrated, Universal Serial Bus (USB) interface.
USB flash drives are typically removable, re-writable and physically much smaller than a floppy disk. A USB flash drive is a portable drive that is same as the size of your thumb that connects to the computer USB port.
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| Pen Drive |
Today, flash drives are available in various storage capacities as 32 GB, 64 GB, 128 GB, 1 TB etc. Flash drives are widely used as an easy and small medium to transfer and store the information from the computers.
