Subject: Computer Basics
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.
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.
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.
Floppy disk are made from Mylar (A plastic materials) coated with magnetic material(Iron Oxide). It is soft magnetic disk and is very thin piece of flexible plastics, also called diskette. It is kept within a plastic jacket and metallic shutter that protects the media access hole. Its storage capacity was 1.4MB. The various sizes of 3.5"ÂÂ, 5.2"ÂÂ, and 8" ÂÂare found.
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:
Magnetic Drum: Drum memory was a magnetic data storage device invented by Gustav Tauschek in 1932 in Austria. It was widely used in the 1950s and into the 1960s as computer memory. Some drum memories were also used as secondary storage. The outer surface of magnetic drum is coated with metal oxide that s used to store binary information.
Secondary storage or memory is the auxiliary storage which hold the data and instructions for long term permanent purpose. They are:
i. Magnetic storage (Disk)
ii. Optical storage (Disk)
iii. Sequential storage
Magnetic disks are direct access storage devices which store data on magnet coated surface for permanently E.g. Hard disk, floppy disk etc.
Auxiliary memory is permanent memory for 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. Examples of auxiliary memory are optical storage, magnetic storage etc.
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