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Hard Disk Drive Components

Basic components of a hard drive. Disk plattersRead/write headsHead actuator mechanismsSpindle motorLogic boardCables

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Hard Disk Drive Components

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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 Cant 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 dont 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 drives 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

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