Mr. Jayanta Dutta, Sr. Trainer, Brainware Skils

1. Hard Disk Drive
Jayanta Dutta

2. Hard Disk Drive (HDD)
Components
• Electromechanical
– Rotating disks
– Arm assembly
• Electronics
– Disk controller
– Cache
– Interface controller

4. Hard Disk Drive Components
• Disk platter
• Read/Write head
• Head arm/Head slider
• Head actuator mechanism
• Spindle motor
• Logic board
• Air filter
• Cables & Connectors

5. HDD Organization
Arm
Assembly
Arm Head
CylinderSpindle
Platter
Track

6. HDD Organization
• Typical configurations seen in disks today
– Platter diameters: 3.7”, 3.3”, 2.6”
– RPMs: 5400, 7200, 10000, 15000
• 0.5-1% variation in the RPM during operation
– Number of platters: 1-5
– Mobile disks can be as small as 0.75”
• Power proportional to: (# Platters)*(RPM)2.8(Diameter)4.6
– Tradeoff in the drive-design
• Read/write head
– Reading – Faraday’s Law
– Writing – Magnetic Induction
• Data-channel
– Encoding/decoding of data to/from magnetic phase changes

7. • Disk platter

8. • Substrate
 The material by which a disk platter is
manufactured
o Aluminum
o Glass or Glass Ceramic compounds
 To hold the data on the substrate, it
must be coated with magnetic media
o Iron Oxide media
o Thin Film media

9.  Iron Oxide media
It gives around 30 meu inch
thickness
 Looks brown or amber in colour
Semi liquid coating of the iron oxide
compound
 Thin Film media
 Very thin coating
 Only 1-4 meu inch thickness
It is coated over the substrate by using
two types of process

10. Storage Density
• Determines both
capacity and
performance
• Density Metrics
– Linear density
(Bits/inch or BPI)
– Track density
(Tracks/inch or TPI)
– Areal Density =
BPIxTPI
BPI
TPI

11. Read / Write heads
• Ferrite heads
• MIG heads
• TF heads
• MR/AMR heads
• GMR heads
• CMR heads
• TMR heads

12. Ferrite heads
 For Winchester disks
Made of iron oxide core wrapped with electro
magnetic coils
It is a u shaped iron core wrapped with electrical
windings
 They are not so small in size
 Used in hard disk up to 50 MB

14. Metal –In- Gap head
 Same design as ferrite heads
Added a special metallic alloy on the head
Usually found in hard disks of about 50
MB – 100 MB

15. Thin Film Head
 Very small & light weight heads
Instead of iron oxide, iron nickel alloy core is
used
 Magnetically more powerful
It is costly compared to the other two heads
Usually used in hard disks of 100 – 1000
MB capacities

17. Magneto Resistive Heads
Also known as Anisotropic MR (AMR)
heads
It is the key invention that led to the creation
of hard disks over 1 GB in size
Two separate heads, one for reading & one for
writing on a single assembly
Read head based on MR design & write head
based on Thin film head design
Commonly used in hard disks about 1 GB – 30
GB capacities

19. Giant MR Heads
Works on the same general principles
of MR heads
But uses some what different design that makes
them superior in several ways
 The name “Giant” is not due to the size,
but due to the superior technology
By December 1997, IBM introduced their first hard
disk with GMR heads
 They are more sensitive
GMR are used in latest technology drives
which capacities up to 75 GB

21. Colossal MR Heads
Know the GMR heads are taking over the
market
It is more sensitive & powerful than the GMR
heads
Tunneling MR Heads
It is latest head design which will increase
the areal density too much
 It is still under research

22. Head Arm/Head Slider
The arm on which the Read/Writehead
is located
The size of a slider in a 3.5” size hard
disk is 0.08*0.063*0.017 inch
 Slider of this size is called “Nano Slider”

23. Spindle Motor
It is the main motor which rotates the
hard disk drive platter
It is called Spindle motor because it is
directly connected to the Spindle on which
the platters are connected
Spindle motor rotates at a speed of
3600 to 7200 RPM or more

24. Logic Board
An intelligent circuit board is in builtto
the hard disk in the modern days
It contains the electronic components
that controls various sections of the hdd
It also acts as an interface between the
hard disk drive and the computer

25. Air filter
 To filter the air
 Most hdd will have two air filters
 The two air filters are
One is called the Recirculating Air
filter & the second one is called
Breather filter

26. Cables & Connectors
Cables & connectors are used to connect the
hdd to the main computer system
 Data/Control interface cable of 40 pins
 A 4 pin Molex power connector
Head Actuator Mechanism
The Read/Write head is moved on the
platter using a mechanism
 Two types of head actuator mechanism
They are stepper motor actuator & voice
coil actuator

27. Stepper Motor Actuator
 It is a motor which rotates in steps
 Stepper motor turns in a fixed angle
 The smallest fixed angle is called a “detent”
The stepper motor is connected to the R/W
head by using two mechanism
They are Split metal band mechanism
& Rack and pinion gear mechanism

28. Voice Coil Actuator
In the voice coil actuator head moves in
& out in a straight line
 It is more faster and accurate
Stepper motor is used in the Open loop
disk drive and the Voice coil actuator is
used in the closed loop disk drive

29. Disk Geometry
To arrange the data on the disk surface, the
disk surface is divided in to different sections
called Tracks, Sectors, Cylinders, Sides etc
 Two types of disk geometry
 Physical geometry & Logical geometry

30. Sides/Heads
Each platter of a hard disk will have two sides
 Each side will have each heads
 Total no of sides = Total no of heads
When addressing either, heads or sides is denoted
 Total no of heads may range from
2-256 (in logical geometry)
Total no of sides may range from 2-20(in
physical geometry)
 The head numbering starts from 0-…..
It starts from the uppermost of the platter

31. Tracks
Each side of the platter’s surface is divided in to
so many concentric circles
 The track numbering starts from 0-….
The outermost tracks is given the track number 0
and next 1, next2 and so on
The innermost track will have the highest
number
No of tracks on a platter may range from 300-
3000
Modern hard disk will have thousands of tracks
on each platter

32. Sectors
 It is the smallest unit of data storage (in
physical geometry)
 It can hold up to 512 MB of data only
The sector numbering starts from 1-….
The storage capacity of the hdd will vary
according to the no of sectors/track present in
it

34. Cylinders
Same tracks on different platters or sides
forms an imaginary cylinder
 In a hard disk the data is stored in a
cylinder by cylinder method
The reason is due to the single head assembly
 A track & cylinder are two different
things, but they are used simultaneously
Total no of tracks on a side = Total no of
cylinders
 The cylinder numbering starts from 0-….
 It starts from the outermost of the platter

36. Clusters
 A group of sector is calledClusters
It is the smallest unit of data storage which can
identified by the operating system

37. Seeking
Zone Bit Recording
Interleave Factors Head
Skewing Cylinder
Skewing Head Parking

38. Seeking
• Seek time depends on:
– Inertial power of the arm actuator motor
– Distance between outer-disk recording radius and inner-
disk recording radius (data-band)
• Depends on platter-size
• Components of a seek:
– Speedup
• Arm accelerates
– Coast
• Arm moving at maximum velocity (long seeks)
– Slowdown
• Arm brought to rest near desired track
– Settle
• Head is adjusted to reach the access the desired location

39. Zoned-Bit Recording
• Outer tracks can hold more sectors due to
larger perimeter
• Per-track storage-allocation requires
complex channel electronics
• Tradeoff:
– Group tracks in zones
– Outer zones allocated more sectors than inner
ones
– Due to constant angular velocity, outer zones
experience higher data rates.
• Modern disks have about 30 zones

40. Zone bit recording

41. Interleave
• If the sectors are numbered sequentially
from 1 - max number, the disc read
operation will be very slow
• Consider disc read of a complete track
(sectors1 ,2,3 etc)
• The drive starts reading when R/W head
reaches Sector1
• After reading, drive sends this data to the
controller. CRC test is done. During this
the disk is rotating

42. Interleave
• By the time this process is
completed, the R/W disk passes the
2nd sector.
• Now when the 2nd sector instruction
is given, the head is in the 3rd / 4th
sector. Now the disc has to complete
one full rotation to come to 2nd
sector again
• This will make the read process slow

43. Interleave Factor
• The solution to this to put the 2nd sector in 3rd or
4th position, so that the head will position itself
at the correct location when it receives the
instruction to read the 2nd sector
• Numbering the sectors out of order with
leaving a gap of one or more sectors in
sector numbering is called Interleaving.
• Now a days , we have 1:1 interleave with
IDE and SCSI interfacing which support
them

44. Interleave factor

45. Track Skewing
• To provide faster sequential access
across track and cylinder boundaries
• Skew logical sector zero of each track
by worst-case head/track switch-time
• Each zone has different skew factors

46. Park & Lock Head
Crashes
Floating Height/Head Gap Formatting
Types Of Formatting
Low Level Formatting
High Level Formatting
Re-Formatting/Re-Initializing

47. Partitioning
• It was a new concept introduced by IBM
when they launched 10 MB HDD
• At that time 10 MB was considered to be a
large storage area and decided to use it for
2 different operating system
• Partitioning means dividing the drive into
logical parts or volumes
• DOS/ Windows FDISK.EXE is used to
partition a HDD. Big size partition is
wastage of space

48. Partitioning
Consider the table:
• If partition size is 100 MB
– Cluster size is 2 KB
• For partition size 4000
MB – cluster size is 64 KB
• On 100 MB disc – 500 files
will require 500x 2 KB =
1MB of space
• On 400MB disc 500 files
will require 500 x 64 KB =
32MB of space
Size of
logical Drive
(MB)
Cluster size
in KB
0-15 4
16- 127 2
128 -255 4
256 -511 8
512 - 1023 16
1024 – 2047 32
2049- 4095 64

49. Partition
• Partitioning is the middle process
Configure the system BIOS setup
Low level formatting
Partitioning (FDISK)
High level formatting

50. Partitioning
• It is done to have more than one operating system
on the same drive
• To have more than one logical drive
• Partition program FDISK writes a MBR in the
first physical sector i.e Cylinder 0, head 0 and
Sector 1
FDISK can be used for :
• Creating a primary DOS partition
• Creating an extended DOS partition
• Creating logical drives in extended partition
• Deleting partitions
• Display partition data

51. Hard Disk Interfaces
 ST-506/412
 ESDI (Enhanced Small Disk Interface)
 IDE (Integrated Drive Electronics)
 EIDE (Enhanced integrated drive electronics)
 SCSI ( Small Computer System Interface)