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Tuesday, 7 July 2015

Hardware: Hard Disk Drive

Hard Disk Drive (Hard Drive)

aka HD, HDD
b.  1956

=  two sizes:

*  5.25 in  - desktop
*  3.50 in  - laptop

Must be 100% dust-free
Encased:  platters sealed in airtight case (partially in vacuum)
Sealed chamber = 'hard disk assembly' (HDA)

Consists of:
  • Case
  • Chassis
  • Controller / Circuitboard ('middle man' between Actuator & OS)
  • Actuator
  • Read/Write Actuator Arm
  • Read/Write Heads
  • Spindle (at centre)
  • Platter(s)
  • (multiple platters form a 'cylinder')
  • connected to Motherboard (via ATA, SCI or SATA cable)
    *powered by PSU (power supply unit, on back of HDD via circuitboard (Disk Controller)
Platters

Platter = flat, round,discs

base material must be non-magnetic
base material usually aluminium or ceramic/glass
base material - glass increasingly used (heat resistance / thinner)

base material must be capable of being machined/polished smooth
base material, glass trending (heat resistance + makes thinner platters)

Platter both sides of platter coated with magnetic surface
  • formerly:  magnetic oxide
  • now:  thin-film medium (magnetic metal)
Two or three platters are stacked
in between:  gap for read/write heads (mounted on end of actuator arm)
Read/write head for each side of each platter
Read/write head moves from outer edge of platter towards centre/spindle.
Platters share common 'spindle'
Spindle turns platters at rate of abt several 1,000 revolutions per min
Read/write heads hover, abt 0.07mm away from platter surface
Read/Write Heads

Read/write heads rest on platters
(when PC powered down & drive stops spinning)

Read/write heads rest on dedicated area (no data stored):  'landing zone' (LZ)
HD lives in the 'drive bay'.
HD connected to Motherboard, via ATA, SCI or SATA cable connections
HD powered by PSU (power supply unit)
On back HD = circuitboard (disk controller (DC), data sent to/from HD via DC)

OS examines HD FAT (file allocation table)
FAT = location & available HD areas info
Disk controller directs actuator to move & align R/W heads
R/W heads deal in binary info (zeros + ones)

Solid State Drives (SSDs)
are the go currently
*HDD remains in use desktops (b/c superior storage capacity)
HD unit positioned in:  'drive bay' (an allocated spot)



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SOURCE

http://www.pctechguide.com/hard-disks/hard-disk-hard-drive-construction

http://www.computerhope.com/jargon/h/harddriv.htm


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