1. Introduction to Hard Disk Drive
PPT BY VISHAL GARG
CSE 5TH SEMESTER
SHIVALIK COLLEGE OF
ENGINEERING

2. Outcomes
 What is Hard Drive
 Geometry of Hard Drive
 Hard Disk’s Parts & their Functions
 Characteristics of Hard Disk
 How Hard Drives Work
 Hard Drive Interfaces
 What is hard disk partition
 Why make partitions

3. What is a Hard Drive ?
 The hard drive is one of the most important parts of computer because it is
used as a long-term storage space for our data.
 What that means, is regardless of whether or not the computer is on, or
you lose power, the data will still stay stored on this drive keeping it safe.
 A hard drive is an integral piece of our computer as operating system and
all our data are typically stored there.
 In the majority of the situations, if you did not have a working hard drive, or
the hard drive malfunctions, you would not be able to boot your computer
into the operating system and would get an error.

4. Image of a Hard Drive
If you opened your
computer case and
wanted to find your hard
drive, it would look similar
to the image :

5. Inside a Hard Drive
If you will open your hard
drive, which would
immediately void your
warranty and potentially
damage it, you would see
something like the image :

6. Hard Drive Geometry
 Hard disk drives are composed of one or more disks or platters on which
data is stored.
 The geometry of a hard drive is the organization of data on these platters.
 Geometry determines how and where data is stored on the surface of
each platter, and thus the maximum storage capacity of the drive.
There are five numerical values that describe geometry:
 Heads
 Cylinders
 Sectors per track
 Write precompensation(obsolete, but often seen on older drives)
 Landing zone(obsolete, but often seen on older drives)

7. Heads
 The number of heads is relative to the total
number of sides of all the platters used to
store data (see Figure ).
 If a hard disk drive has four platters, it can
have up to eight heads.
 The maximum number of heads is limited
by BIOS to 16.
 Some hard disk drive manufacturers use a
technology called sector translation.
 This allows some hard drives to have more
than two heads per platter.
 It is possible for a drive to have up to 12
heads but only one platter.
 Regardless of the methods used to
manufacture a hard drive, the maximum
number of heads a hard drive can contain
is 16.

8. Cylinders
 Data is stored in circular paths on the
surface of each head.
 Each path is called a track.
 There are hundreds of tracks on the
surface of each head. A set of tracks (all
of the same diameter) through each
head is called a cylinder (see Figure ).
 The number of cylinders is a
measurement of drive geometry; the
number of tracks is not a measurement
of drive geometry.
 BIOS limitations set the maximum
number of cylinders at 1024.

9. Sectors per Track
 A hard disk drive is cut (figuratively)
into tens of thousands of small arcs,
like a pie.
 Each arc is called a sector and holds
512 bytes of data.
 A sector is shown in Figure.
 The number of sectors is not important
and is not part of the geometry; the
important value is the number of
sectors per track.
 BIOS limitations set the number of
sectors per track at 63.

10. Write Precompensation
 All sectors store the same number of bytes: 512; however, the sectors
toward the outside of the platter are physically longer than those closer to
the center.
 Early drives experienced difficulty with the varying physical sizes of the
sectors.
 Therefore, a method of compensation was needed-the write
precompensation value defines the cylinder where write
precompensation begins.
Note :- The write precompensation value is now obsolete, but is often seen on
older drives.

11. Landing Zone
 A landing zone defines an unused cylinder as a "parking place" for
the R/W heads.
 This is found in older hard disk drives that use stepper motors.
 It is important to park the heads on these drives to avoid
accidental damage when moving hard disk drives.

12. Hard Disk’s Parts & their Functions
A hard drive consists of the following:
 Magnetic platters - Platters are the round plates in the image in previous
slide. Each platter holds a certain amount of information, so a drive with a lot
of storage will have more platters than one with less storage. When
information is stored and retrieved from the platters it is done so in concentric
circles, called tracks, which are further broken down into segments called
sectors.
 Arm - The arm is the piece sticking out over the platters. The arms will contain
read and write heads which are used to read and store the magnetic
information onto the platters. Each platter will have its own arm which is used
to read and write data off of it.
 Motor - The motor is used to spin the platters from 4,500 to 15,000 rotations
per minute (RPM). The faster the RPM of a drive, the better performance you
will achieve from it.

13. Characteristics of Hard Disk are:
 Seek Time - The amount of time required to move a drive's read/write
head to a particular location on the disk. The lower the number, the
better.
 Access time - The actual amount of time from when a data is requested
from a drive and delivered. The lower the number, the better.
 RPMS - How fast the platters spin. The higher the number, the faster the
drive will be.
 Capacity - The amount of storage space available on the drive. Typically
most drives purchased today will be 80 Gigabytes or greater. An 80 GB
hard drive will on average cost around 60 USD.
 Interface - How the hard drive connects to your computer. Hard drive's
interface should be supported on your computer before you purchase it.

14. How hard drives work ?
 When the computer wants to retrieve data off of the hard drive, the motor
will spin up the platters and the arm will move itself to the appropriate
position above the platter where the data is stored.
 The heads on the arm will detect the magnetic bits on the platters and
convert them into the appropriate data that can be used by the
computer. Conversely, when data is sent to the drive, the heads will this
time, send magnetic pulses at the platters changing the magnetic
properties of the platter, and thus storing your information.
Note : It is important to note, that since the data stored on your hard drive is
magnetic, it is not a good idea to play with a magnet near your hard drive.

15. Hard Drive Interfaces
 A hard drive connects to your computer through a specific type of
interface. The interface on your hard drive must match the corresponding
interface on your motherboard.
Some information about interfaces are explained below.
 IDE or ATA - This is currently the most common interface used but is quickly
becoming overcome by the newer SATA interface. Hard drives using this
type of interface have speeds up to 100 Mbps.
 SATA - A newer interface that uses less bulky cables and has speeds
starting at 150 Mbps for SATA and 300 Mbps for SATA II. Almost all
computer manufacturers have started using SATA drives.
 SCSI - This type of interface is typically used in a business environment for
servers. Hard Drives designed for a SCSI interface tend to have a faster
RPM which therefore provides better performance.

16. What is a hard disk partition ?
 When a hard drive is installed in your computer, it must be
partitioned before you can format and use it.
 Partitioning a drive is when you divide the total storage of a drive
into different pieces. These pieces are called partitions.
 Once a partition is created, it can then be formatted so that it can
be used on a computer.
 When partitions are made, you specify the total amount of storage
that you would like to allocate to that partition from the total size of
the drive.

17. Why make partitions ?
There are following reasons of making partitions :
 Multiple Filesystems - When you create a partition, then you need to
format it before it can be used.
 When formatting a partition you tell the operating system what filesystem
you would like that partition to be formatted in.
 Once you format a partition, and therefore assign the type of filesystem
you want to use with it, you can not change that filesystem without
formatting the partition again and losing all the data contained on it.
 If you require different filesystems on your computer, whether it be for
security or for a specific application, you can then make multiple partition
and assign one type of filesystem to one of the partitions and another to
one of the other partitions.

18. Why make partitions ?(cont…)
 Multiple Operating Systems - Some operating systems use filesystems that
are not compatible with other operating systems.
 If you want to use two operating systems on the same computer that are
not compatible in this way, you could then make two partitions, one for
each operating system.
 Then a boot loader could be used to switch between them when you start
your computer.
 Wasted disk Space -When a filesystems store data in a partition, the larger
the partition, the greater the chance of wasted space.
 By having multiple partitions of smaller size, you reduce the amount of
waste that filesystems may create.

19.  Seperate system files from users files - Some components of an operating
system require storage space to operate.
 For example, in Windows if you have no hard drive space available on the
drive that Windows is installed on, you will not be able to print.
 By creating a partition solely devoted to the operating system and then
another partition dedicated to your own data and programs, there is less
of a chance of you using up the space on the operating system partition
with your data, and thus not causing problems.