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Hard Disk Drive Components
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Page 1: Hard Disk Drive Components

Hard Disk Drive Components

Page 2: Hard Disk Drive Components

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)

Page 3: Hard Disk Drive Components

Head disk Assembly

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

Page 4: Hard Disk Drive Components

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

Page 5: Hard Disk Drive Components

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

Page 6: Hard Disk Drive Components

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

Page 7: Hard Disk Drive Components

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

Page 8: Hard Disk Drive Components

Oxide media

Very sensitive to head-crash during movement of operation

Very few drives use this technology anymore

Page 9: Hard Disk Drive Components

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

Page 10: Hard Disk Drive Components

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

Page 11: Hard Disk Drive Components

Thin-film media

Great chance of survival of this coming into contact with the heads at high speed.

Virtually uncrashable!!!!

Page 12: Hard Disk Drive Components

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

Page 13: Hard Disk Drive Components

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

Page 14: Hard Disk Drive Components

Read/Write Heads

When the drive is spinning, they hover

Page 15: Hard Disk Drive Components

Read/Write Heads

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

Page 16: Hard Disk Drive Components

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

Page 17: Hard Disk Drive Components

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

Page 18: Hard Disk Drive Components

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

Page 19: Hard Disk Drive Components

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

Page 20: Hard Disk Drive Components

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

Page 21: Hard Disk Drive Components

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

Page 22: Hard Disk Drive Components

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

Page 23: Hard Disk Drive Components

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

Page 24: Hard Disk Drive Components

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.

Page 25: Hard Disk Drive Components

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

Page 26: Hard Disk Drive Components

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

Page 27: Hard Disk Drive Components

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

Page 28: Hard Disk Drive Components

Stepper Motors

Variety of problems• Temperature, largest• Can’t compensate for changes in the

track movement due to expansion & contraction

Page 29: Hard Disk Drive Components

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

Page 30: Hard Disk Drive Components

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

Page 31: Hard Disk Drive Components

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

Page 32: Hard Disk Drive Components

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

Page 33: Hard Disk Drive Components

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

Page 34: Hard Disk Drive Components

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

Page 35: Hard Disk Drive Components

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

Page 36: Hard Disk Drive Components

Embedded servo

Every track has its own positioning information as well

Still need a system that offered continuous servo feedback

Page 37: Hard Disk Drive Components

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

Page 38: Hard Disk Drive Components

Dedicated servo

Manufacturer set this up Can tell if drive uses dedicated

servo if it has an odd number of heads.

Page 39: Hard Disk Drive Components

Air filters

Most have two• Recirculating filter - filters small

particles scraped off the platers during takeoffs & landings

• Breather filter - allows for pressure equalization• Heads don’t float if pressure not right

Page 40: Hard Disk Drive Components

Drives are sensitive to temperature

If the drive has been very cold, let it warm up before powering on

Watch humidity

Page 41: Hard Disk Drive Components

Spindle motor

Motor that spins the platters Connected directly to the drive

Page 42: Hard Disk Drive Components

Logic Boards

Mounted on the hard drive Contain electronics that control the

drive’s spindle & head actuator systems & present the data to the controller

Page 43: Hard Disk Drive Components

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)

Page 44: Hard Disk Drive Components

Interface connectors

Most important Carry data & command signals

between the system & the drive

Page 45: Hard Disk Drive Components

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

Page 46: Hard Disk Drive Components

Grounding tab

Provides positive ground connection between the drive & system chassis

Most systems mounted to chassis using screws so ground wire unnecessary

Page 47: Hard Disk Drive Components

Faceplate or bezel

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

Page 48: Hard Disk Drive Components

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

Page 49: Hard Disk Drive Components

Transfer Rate