Hard disk Drive may be defined as PC component that is used for a permanent storage of data. The data stored in the hard disk is not lost by power failure. Hard drives have rigid and round disk which are called platters. These platters are made of aluminum or glass. This is because of these rigid platters that the term hard disk is used. These platters cannot be removed. This is why sometimes called fixed disk drives are.
Hard Disk Drive
Construction.
The two main components of the hard disk drive are the revolving
disks and the heads which read/write the data on the disks. The data is read
and written on tracks as shown below. The tracks as further divided into
sectors, which normally store 512 bytes each.
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| Hard Disk Drive Construction |
All the heads are
mounted on a common carrier device or rack. The heads move radically across the
disk together. They cannot move independently because they are mounted on the
same carrier or rack, called and actuator. Originally, most hard disks spun at
36,000rpm approximately 10 times faster than a floppy disk drive. Most of the
modern drives spin the platters at 42,000 5400; 7200, 10,000 or 15,000rpm. High
rpm disks are normally faster than lower rpm drives. The heads in most hard
disk drives do not (and should not) touch the platters during normal operation.
Tracks
A
track is a single ring of data on one side of a disk.
Sectors
Tracks are divided into several
numbered divisions known as sectors. These sectors represent arc-shaped pieces
of the track. Different type of disk drives split their disk tracks.
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| Tracks & Sectors |
You have to perform following three
steps to make the drive ready for data storage.
1.
Low
Level formatting (LLF)
2.
Partitioning
3.
High
Level Formatting (HLF)
Low Level
Formatting
Low level formats of ATA and SCSI
hard disk drives are performed by the manufacturer and should almost never be
performed by the end user. The only situation when a low level format may be
performed on hard disk drives is that.
1.
When
you need to repair a damaged format (Parts of the disk become unreadable)
2.
When
you wish to wipe away all data on the drive.
First
of all use the Low level formatting utility software provided by the
manufacturers of your hard disk drives. Most manufacturers supply Low level
format programs for their drives.
High Level
Formatting
During the high Level format the
operating system (such as Windows 9x/Me/2000, Windows NT, or DOS) writes the
structures necessary for managing files and data on the disk. High Level formatting is not really a
physical formatting of the drive, but rather the creation of a table of
contents for the disk.
Boot Sector
This sector contains data that
describes the partitions by their starting and ending cylinder, head and sector
locations. The partition table also indicates to the ROM BIOS which of the
partition is bootable and, therefore where to look for an operating system to
load.
Main Hard Disk
Drive Components
May
types of hard disk drives are on the
market, but nearly all share the same basic and physical components. Some
differences might exist in the implementation of these components
(and in the quality of the materials
used to make them) but the operational characteristics of most drives are
similar. The basic components of a typical hard disk drive are as follow.
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| Main Hard Disk Drive Components |
1.
Disk
Platters
2.
Read/write
heads
3.
Head
actuator mechanism
4.
Spindle
motor (inside platter hub)
5.
Logic
board (controller or Printer Circuit Board)
6.
Cables
and connectors
7.
Configuration
items (Such as Jumpers or Switches)
Hard
Disk Platters (Disks)
A hard disk drives has one or more
platters, or disks. Hard disks for PC system have been available in the number
of form factors over the years. Normally the physical size of a dive is
expressed as the size of the platters. Following are the platter sizes that
have been associated with PC hard disk drives.
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| Hard Disk Platters |
1.
3
½-inch
2.
2
1/2-inch
Spindle Motors
The
motor that spins the platters is called the spindle motor because it is
connected to the spindle around which the platters revolve. Spindle motors in
hard disk drives are always connected directly, no belts or gears are involved.
The platters in hard disk drives revolve at speed ranging from 3600rpm to
15000rpm or more.
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| Spindle Motors |
Logic Boards
All hard disk drives have more or
more logic boards mounted on them. The logic boards contains the electronics
that control the drive’s spindle and head actuator systems and present data to
the controller in some agreed upon form.
In
many cases, logic boards plug into the drive and are easily replaceable. These
boards are usually mounted with standard screw hardware. If a drive is failing
and you have a spare you might be able to verify a logic board failure by
taking the board off the known good drive and mounting it on the bad one.
Cables and
Connectors
Most of the hard disk drives have at
least these two types of connections
1.
Interface
connector(s)
2.
Power
connector
IDE (Integrated
Drive Electronics) Interface
IDE stands for Integrated Drive
Electronics. Integrated Drive Electronics refers to the fact that
the interface electronics or controller is built into the drive and is not a
separate board, as with earlier drive interfaces.
The actual name of interface is ATA
(AT Attachment). This name was to it as the combined drive and controller were
designed to connect to the IBM AT computer. ATA is used to connect not only
hard disks, but also CD-ROM and CD RW drives, DVD Drives and tape drives. ATA
originally referred to a hard disk drive that plugged directly into a version
of the AT bus more commonly known as the 16bit ISA bus. There are many types of
IDE interface variations before the ATA IDE interface was developed with its
present specifications. ATA IDE is the interface we will study in the following
section.
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