Functions of hard disk

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Hard Drive / Hard Disk

• Functions of hard disk
• - Hard disk is used to store the large size of
  application
• programs or files.
• - It provide larger storage capacities and much
  faster access times than floppy disks.
• Characteristics of Hard disk
• Like a floppy disk, a hard disk is a type of
  magnetic
• media that stores items using magnetic
  patterns.
• Also as read / write storage media.

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• Hard disk structure
• A hard disk consist of five major components as
• i) magnetic platter
• ii) spindle
• iii) read / write head
• iv) head actuator
• v) circuit board
• How the hard disk works
• Platters
• Most hard disk have multiple platters stacked on
  top of one another and each platter has two read
  / write heads.

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• example
• If a hard disk has 5 platters, then it will
  
• have 10 read / write heads
• The hard disk has arms that move the read / write
  heads to the proper location on the platter
• 2) Cylinder
• - Cylinder is the location of a single track
  through all platters on a hard disk.
• The read / write heads often referred to by its
  cylinder instead of its track.

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• 3) Sector
• Every tracks have numbers of sector.
• Sector is define which area it placed on the
  platter, track number and sector number on every
  track.
• Sector number consist of 0 and 1 because each
  platter only has 2 sides.

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• example
• If a hard disk has 4 platters (8 sides),
• each side with 1000 tracks ( 1000
  
• cylinders consisting of
  eight tracks )
• Note Assume eight tracks two sides for each
  platters

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• Sequence of hard disk works
• Step 1 The circuit board controls the movement
  of
• the head actuator and a small motor.
• Step 2 A small motor spins the platters the
  entire time
• the computer is running.
• Step 3 When software requests a disk access, the
  
• read / write heads move to the FAT
  to
• determine the current or new
  location of data.
• Step 4 The head actuator positions the read /
  write
• head arms over the correct location
  on the
• platters to read or write data.

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• Hard disk speed and storage capacities
• How to define the size of a hard disk?
• - It depends on the geometry and sizes of sector.
• Eg. A hard disk has 723 cylinders (1 cylinder
  51 sector, 1
• sector 0.5 KB),7 platters and 14 read /
  write heads
• Storage capacities formula
• (Byte / sector) x (sector / cylinder) x
  numbers of cylinder
• x numbers of read / write head
• (0.5 / 51) x (51 / 1) x 723 x 14 258,111
  KB (258 MB)
• with speed rate 5400 to 7200 RPM (revolution
  per minute)

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• Removable Hard Disks
• What is?
• The device that can be removed and inserted from
  a hard disk drive.
• Much like floppy disk, pen drive, pocket drive
  and Jaz disk.
• Advantages of the removable hard disk
• To transport a large number of files
• To make back up copies of important files
• For data security issued

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• Removable hard disk also used as Disk Pack that
  commonly use in network environment, mini
  computers and main frame computer.
• - Although disk pack is a collection of
  removable hard disk mounted in the same cabinet
  as the computer or enclosed in the large
  stand-alone cabinet.