hard drive / hard disk
Post on 25-Feb-2016
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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.
Hard Drive / Hard Disk
Hard disk structure- A hard disk consist of five major components as:
i) magnetic platterii) spindleiii) read / write headiv) head actuatorv) circuit board
How the hard disk works1) Platters- Most hard disk have multiple platters stacked on
top of one another and each platter has two read / write heads.
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.
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.
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
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.
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)
Removable Hard DisksWhat 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:1) To transport a large number of files2) To make back up copies of important files3) For data security issued
- 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.
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