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Basic components of a hard drive. Disk plattersRead/write headsHead actuator mechanismsSpindle motorLogic boardCables
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1. Hard Disk Drive Components
2. 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)
3. Head disk Assembly Platters, spindle motor, heads, & head actuator mechanisms usually contained in this sealed chamber
4. 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
5. 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
6. 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
7. 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
8. Oxide media Very sensitive to head-crash during movement of operation
Very few drives use this technology anymore
9. 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
10. 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
11. Thin-film media
Great chance of survival of this coming into contact with the heads at high speed.
Virtually uncrashable!!!!
12. 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
13. 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
14. Read/Write Heads When the drive is spinning, they hover
15. Read/Write Heads Four types of read/write head designs:
Ferrite
Metal-In-Cap
Thin-film
Magneto-resistive
16. 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
17. 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
18. 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
19. 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
20. 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
21. 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
22. 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
23. 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
24. 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.
25. 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
26. 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
27. 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
28. Stepper Motors Variety of problems
Temperature, largest
Can’t compensate for changes in the track movement due to expansion & contraction
29. 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
30. 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
31. 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
32. 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
33. 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
34. 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
35. 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
36. Embedded servo Every track has its own positioning information as well
Still need a system that offered continuous servo feedback
37. 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
38. Dedicated servo Manufacturer set this up
Can tell if drive uses dedicated servo if it has an odd number of heads.
39. 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
40. Drives are sensitive to temperature
If the drive has been very cold, let it warm up before powering on
Watch humidity
41. Spindle motor Motor that spins the platters
Connected directly to the drive
42. Logic Boards Mounted on the hard drive
Contain electronics that control the drive’s spindle & head actuator systems & present the data to the controller
43. 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)
44. Interface connectors Most important
Carry data & command signals between the system & the drive
45. 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
46. Grounding tab Provides positive ground connection between the drive & system chassis
Most systems mounted to chassis using screws so ground wire unnecessary
47. Faceplate or bezel Page 754, fig 12.11
Part of case, not the drive
48. 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
49. Transfer Rate