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 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: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.