Computer Secondary storage devices

SECONDARY STORAGE DEVICES

Are of two types-sequential access devices(ex-Magnetic tape) and direct access devices(ex-Magnetic disks,optical disks and memory storage devices).

SEQUENTIAL AND DIRECT ACCESS DEVICES

There are two methods of accessing information-sequential or serial access,and direct or random access.
 

MAGNETIC TAPES

Magnetic tape is a medium for magnetic storage,made of a thin,magnetizable coating on a long,narrow strip of plastic film.It was developed in Germany in 1928,based on magnetic wire recording.It is used to capture speech and music.

Storage capacity of a tape:-

Data recording density × Length

Types:-

Half-inch tape reel, Half-inch tape cartridge, Quarter-inch streamer tape and 4mm digital audio tape(DAT).
Advantages:
  • Secure
  • Safe
  • Cost effective and flexible.
 

MAGNETIC DISKS

A magnetic disk is a storage device that uses a magnetization process to write,rewrite and access data.A magnetic disk is a thin,circular plate/platter of metal or plastic.It is used to store computer data as well as audio and video signals.
Storage capacity of a disk system=Number of recording surfaces
                               × Number of tracks per surface
                               × Number of sectors per track 
                                 × Number of bytes per sector 
Types:-
  • Floppy disks
  • and Hard disks.

Floopy disk-

The floppy disk drive,also known as diskette,is a removable magnetic storage medium that allows recording of data.

Hard disk

Hard disk are the primary on-line secondary storage device.It is a hardware component that stores all of your digital content.Type:-Zip/Bernoulli disks, disk packs and Winchester disks.

OPTICAL DISKS

An optical-disk storage system consists of a metallic or plastic disk coated with a highly reflective material.It uses laser beam technology for reading/writing of data from/to disk surface. Optical disks are also known as laser disks or optical laser disks. 

Storage capacity of an optical disk=Number of sectors × Number of bytes per sector
 
Types:- All optical disks are round platters.
  • CD-ROM(Compact Disk-Read-Only Memory)
  • WORM(write-once,read-many) DISK/CD-RECORDABLE(CD-R) DISK
  • CD READ/WRITE(CD-RW) DISK

DIGITAL VIDEO(OR VERSATILE) DISK(DVD)-

Types:

  • DVD-ROM
  • DVD-RAM
  • DVD-R
  • and DVD-RW.
Advantages:-
  1. Mass storage capacity
  2. Low cost
  3. Long media life
  4. and high data stability.
 

MEMORY STORAGE DEVICES:-

Any type of computing hardware that is used for storing,porting or extracting data files and objects.
Types:-
  • Flash Drive(Pen Drive)
    Flash drive is a compact device of the size of a pen.It is a portable computer drrive that uses flash memory.
  • Memory Card (SD/MMC)
    It is a type of storage device that is used for storing media and data files.It is used in mobile phones to store information like photos and music,as well as in camcorders to store video.
 

MASS STORAGE DEVICES:-

Refers to ordinary storage,which was always larger that main memory(RAM).
TYPES:-
  • Disk Array
    It is a disk storage system which contains multiple disk drives.It is used for block-based storage,file-based storage or object storage.
  • Automated Tape Library
    It allows you to use system-managed storage for mountable tape cartridges.It is used for storing,retrieving,reading from and writing to tape cartridges.It uses a set of magnetic tapes.
  • CD-ROM Jukebox
    A CD-ROM reader designed for network use.It uses a set of CD-ROMs.
  • Access Time
    It is the time from the start of one storage device access to the time when the next access can be started.
 

ON-LINE,NEAR-LINE AND OFF-LINE STORAGE

Online storage is immediately available for input/output(I/O). Nearline storage is not immediately available,but can be made online quickly without human intervention. Offline storage is not immediately available and requires some human intervention to become online.
 

HIERARCHICAL STORAGE SYSTEM (HSS)

HSM is a storage system that automatically moves data between tiered storage devices depending on performance requirements.   
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