# Hard Drive Hard Disk Functions of hard disk

• Slides: 14

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.

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 1) 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 files 2) To make back up copies of important files 3) 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.