Auxiliary Memory

Auxiliary memory is used as permanent storage of data. The data and instructions are supplied to primary memory from auxiliary memory. They are used for storing system program, large data files and other back up information. This is called non-volatile memory and can store tremendous amount of data, e.g. Optical storage, magnetic storage.

Optical storage Devices

CD- ROM (Compact Disk Read Only Memory):

It is read only optical storage medium and are capable of holding about 700mb of data. Accessing data from CD- ROM is very fast than floppy disk but considerably slower than modern hard disk. The disk is made up of polycarbonate wafer, 120 mm in diameter and 1.2 mm thick with a hole of 15mm in the middle. The wafer base is coated with metallic film usually an aluminum alloy. The aluminum film is covered by a plastics poly carbonate coating that protects the underlying the data. In CD- ROM, data and instructions are represented in form of land and pits. The lights are reflects from the land and diffused from pits.

CD- RW (Compact Disk- Read/ Write Memory): CD-RW (Compact Disc-ReWritable) is a digital optical disc storage format. A CD-RW disc is a compact disc that can be written, read arbitrarily many times, erased and written again. The technology was introduced in 1997. In CD- RW, the change of state i.e. the formation of land and pit is not permanent. Laser is used to heat the active material in CD-RW to liquid state to create required land and pits to save the data.

Digital Versatile Disk (DVD): It is the improved version of CD-ROM, i.e. it can store multiple times more data in the same sized disk. This is possible due to the reduction in the size of land and pit. So bits are packed more closely on DVD then CD- ROM. They are available as DVD-ROM, DVD-RW.

Blue Ray Disk: It is the latest optical storage medium more sophisticated than DVD. It was developed mainly to store High Definition Video (HD Video), Video games and other data that are more than 2.5 GB. The name Blu-Ray is derived from blue laser used to read/write the disk. It was developed by Blu-Ray Disk Association and MIT.

Magnetic Storage Devices:

The magnetic devices use principle of electromagnetism for storing and receiving data. The surface of magnetic devices is coated with magnetic material, the lightening process done by using READ/ WRITE ARM. The Surface of storage device produces small current to flow which is sensed by Read/write arm and is sent o main memory, e.g. Hard Disk, Magnetic tape, Magnetic Drum, etc.

Hard Disk Drives: HDDs were introduced in 1956 as data storage for an IBM. It contains rigid, disk shaped platters, constructed from Aluminum or glass. The physical construction of hard disk consists of spinning disks with heads that moves over the disks and stores data in tracks and sector. The heads read and write the data in concentric circles called tracks which are divided into segments called sectors. They have multiple spinning disks called platters which are stacked on top of each other. The actuators move the read and write head at required position in platters.

Magnetic tape: It is made from plastics ribbon coated with metal oxide or magnetic material. It uses the principle of magnetism and diamagnetisms to store and erase data for recording data. It uses head which intermits the magnetic field and non- magnetic field. Magnetic tapes are available in 1.2", 1, 8" mm in sizes, etc. Information is stored in tracks of each tape. Tracks are again divided into blocks and each block can store data ranging from 512 and above bytes. Magnetic tapes are used as offline back up because of following reasons:

1. Safety from fluctuation of electric supply.
2. Safety from erasing file mistakenly.
3. Safety from failure of hardware.
4. Safety from damage of computer by storm, flood, fire, etc.

Things to remember

• Auxiliary memory is also called auxiliary storage and is used to store data permanently.
• Optical storage devices include CD-ROMS, CD-RW, DVDs and Blu-ray Disks.
• Magnetic storage devices include, Hard disk drives, Floppy disks, Magnetic tapes and magnetic drums.
• A CD-RW disc is a compact disc that can be written, read arbitrarily many times, erased and written again.
  
• The magnetic devices use principle of electromagnetism for storing and receiving data.
  

• It includes every relationship which established among the people.
• There can be more than one community in a society. Community smaller than society.
• It is a network of social relationships which cannot see or touched.
• common interests and common objectives are not necessary for society.

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