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 • 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: • To transport a large number of files • To make back up copies of important files • 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.