Hard Disk Drive Components

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Hard Disk Drive Components
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Basic components of a hard drive

• Disk platters
• Read/write heads
• Head actuator mechanisms
• Spindle motor
• Logic board
• Cables connectors
• Configuration items (such as jumpers switches)

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Head disk Assembly

• Platters, spindle motor, heads, head actuator
  mechanisms usually contained in this sealed
  chamber

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Hard Disk Platters

• Hard disks have been a number of different form
  factors over the years
• 3 1/2 inch drives are the most popular for
  desktop some portables
• Max number of platters in a 3 1/2 inch drive is 11

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Hard Disk Platters

• Traditionally made from aluminum alloy
• Desire for higher density has led to the use of
  platters made of glass (glass ceramic composite)
• Glass platters offer greater rigidity more
  stable thermally

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Hard Disk Platters

• No matter what type of platter is used, the
  platters are covered with a thin layer of
  magnetically retentive substance (called the
  medium) on which magnetic information is stored.
• Oxide media
• Thin-film media

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Oxide media

• Made of various compounds, oxide being the
  primary active ingredient
• Put on the disk like syrup, coating the entire
  disk
• Coating is approx 30 millionths of an inch and is
  made smooth
• Platters appear to look brownish or amber

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Oxide media

• Very sensitive to head-crash during movement of
  operation
• Very few drives use this technology anymore

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Thin-film media

• Thinner, harder more perfectly formed than
  oxide media
• High-performance medium that enabled a new
  generation of drives to have lower head floating
  heights, which in turn made increase in drive
  density possible

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Thin-film media

• Coating is put on the platter using an
  electroplating mechanism, similar to that of
  putting chrome plating on the bumper of the car.
• Looks silver like the surface of a mirror

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Thin-film media

• Great chance of survival of this coming into
  contact with the heads at high speed.
• Virtually uncrashable!!!!

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Read/Write Heads

• See diagram on page 736, fig. 12.6
• A hard disk has one read/write head for each side
  of the platter
• The heads are connected on a single movement
  mechanism
• They move in unison

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Read/Write Heads

• Each head is on an actuator arm that is
  spring-loaded to force the head into contact with
  a platter
• The heads float only a very slight distance above
  the platter
• When the drive is at rest, the heads are forced
  into direct contact with the platters by spring
  tension

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Read/Write Heads

• When the drive is spinning, they hover

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Read/Write Heads

• Four types of read/write head designs
• Ferrite
• Metal-In-Cap
• Thin-film
• Magneto-resistive

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Ferrite

• Virtually obsolete
• Had an iron-oxide core wrapped by passing a
  magnetic field near them
• Heads were large heavy
• Required a much higher floating height than today

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Metal-In-Gap

• Enhanced version of the ferrite heads
• Virtually obsolete
• Have a layer of magnetic alloy, which increased
  the magnetization capability allowed the heads
  tow rite at higher densities

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Thin Film

• Created through a photolithographic process
• Manufactured in the same manner as a
  semiconductor
• Very narrow controlled head gap that is created
  by sputtering (a process of spreading material
  very thinly on a surface) a hard aluminum material

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Thin Film

• The material completely encloses the gap
  protects the area
• Head is very light can float much closer to the
  platters than previous technologies
• Writes at much higher densities
• Magneto-resistive technology taking over

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Magneto-Resistive

• Latest in technology highest performance
  available
• As areal density increases (technology growth
  rate indicator), TF and MIG will disappear
• Relies on the fact that the resistance of a
  conductor changes slightly when an external
  magnetic field is present

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Magneto-Resistive

• Two heads in one - MR heads do not write
• They are sensors for reading
• The heads have two separate elements
• TF for writing
• MR for reading
• Each head optimized for its task

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Magneto-Resistive

• How do they read?
• MR heads use a property discovered to exist in
  most conductive materials
• Their resistance changes when exposed to a
  magnetic field
• Special alloys are chosen for use due to the
  magnitude of their resistance change in the
  presence of a magnetic field

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Head Sliders

• Describes the body of material that supports the
  actual drive head itself.
• This actually floats or slides over the surface
  of the disk, carrying the head at the correct
  distance from the medium for reading writing

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Head Sliders

• Most resemble a catamaran, with two outboard pods
  that float along the surface of the disk media
  a central rudder portion that actually carries
  the head the read/write gap.

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Head Actuator Mechanisms

• Moves the heads across the disk positions them
  accurately above the desired cylinder
• Two basic categories
• Stepper Motor actuators
• Voice coil actuators

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Head Actuator Mechanism

• A drive using a stepper motor is much less
  reliable than one using a voice coil
• See page 741, Fig. 12.7
• Floppy drives use a stepper motor to position
  their heads
• Accuracy of the stepper is suited to a floppy
  drive, because track densities usually lower

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Stepper Motors

• An electrical motor that can step or move from
  position to position, with mechanical dents or
  click-stop positions.
• Can only stop at predetermined spots
• Motors sealed outside of the head disk assemble,
  although the spindle of the motor penetrates the
  head disk assembly through a sealed hole

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Stepper Motors

• Variety of problems
• Temperature, largest
• Cant compensate for changes in the track
  movement due to expansion contraction

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Voice Coil

• Used in almost all hard drives today
• Uses feedback signal from drive to accurately
  determine head positions adjust them
• Works by pure electromagnetic force
• Similar to construction of a typical audio speaker

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Voice Coil

• Audio speaker uses a stationary magnet surrounded
  by a voice coil which is connected to the
  speakers paper cone
• When the coil is energized, it moves produces
  sound from the cone

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Voice Coil

• In a typical hard disk, the electromagnetic coil
  is attached to the end of the head rack placed
  near a stationary magnet
• There is no physical contact between the coil
  the magnet
• It moves by electromagnetic force
• This force moves the head rack

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Voice Coil

• Use a servo-mechanism to move to the desired
  position on the disk
• Stepper motors move to predetermined spots
• Not affected by temperature
• Automatic head parking
• Heads are positioned by magnetic force, so when
  power removed, mag field disappears heads stop

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Servo Mechanisms

• Controls voice coil positioners
• Three
• Wedge servo
• Embedded servo
• Dedicated servo
• These enable the head positioner to
• adjust continuously to be precisely above a given
  cylinder on the disk

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Wedge servo

• Page 746, fig 12.8
• Older technology
• Touchy with configuration and controller
• Needed several revolutions before it could
  accurately determine adjust head position
• No longer in use

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Embedded servo

• Page 747, fig 12.9
• Writes the servo information before the start of
  each sector
• Allows for positioner circuits to receive
  feedback many times in a single revolution
• Much faster accurate positioning

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Embedded servo

• Every track has its own positioning information
  as well
• Still need a system that offered continuous servo
  feedback

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Dedicated servo

• Servo information is written continuously
  thoughout the entire track, rather than just once
  per track or at the beginning of each sector
• Uses one side of one of the platters exclusively
  for servo-positioning information

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Dedicated servo

• Manufacturer set this up
• Can tell if drive uses dedicated servo if it has
  an odd number of heads.

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Air filters

• Most have two
• Recirculating filter - filters small particles
  scraped off the platers during takeoffs
  landings
• Breather filter - allows for pressure
  equalization
• Heads dont float if pressure not right

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• Drives are sensitive to temperature
• If the drive has been very cold, let it warm up
  before powering on
• Watch humidity

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Spindle motor

• Motor that spins the platters
• Connected directly to the drive

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Logic Boards

• Mounted on the hard drive
• Contain electronics that control the drives
  spindle head actuator systems present the
  data to the controller

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Cables Connectors

• Sever connectors for interfacing to the computer,
  receiving power sometimes grounding to the
  system chassis
• Three types
• Interface connectors
• Power connectors
• Option ground connector (green wire)

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Interface connectors

• Most important
• Carry data command signals between the system
  the drive

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Power Connector

• Usually same 4-pin connector type that is used in
  a floppy disk drive
• Same power-supply connector plugs into it
• Most use both 5 12 volt power
• Red, yellow, 2 black with keyed white end

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Grounding tab

• Provides positive ground connection between the
  drive system chassis
• Most systems mounted to chassis using screws so
  ground wire unnecessary

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Faceplate or bezel

• Page 754, fig 12.11
• Part of case, not the drive

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Speed of the Drive

• Average Seek time
• Page 756
• Measured in milliseconds - average amount of time
  it takes to move the heads from one cylinder to
  another cylinder a random distance

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Transfer Rate