Um-e Habiba

1. Um-e Habiba Roll # 16 Mphill 2013-2015 07 Jan 2014

2. Hard Disk Drive (HDD) (construction and working)

3. Contents • Introduction • Working Principle • Working • Geometry • Construction

4. Introduction • HHD or Hard disk drive is storage device with fixed high density, non volatile data storage • It is rigid media composed of relatively inflexible Aluminum or glass platters or disk. This inflexibility led to name hard disk. • Hard disk drive is fixed, not removable • Invented in 1950’s, as large disks holding just few MB data • Use magnetic recording techniques

5. Working Principle • Works on principle of Electromagnetism • While Writing data ----Magnetic induction • Reading data --- Faraday’s law • Data is stored in digital form, in the form of bit cells • Each bit cell composed of magnetic grains • 0 represent regions of grains of uniform boundary • 1 represents boundary between regions of opposite magnetization

6. Writing Process • Data is stored on HDD in the form of magnetic field • Storage disk is coated with magnetic material, in the absence of B it is un-polarized • When is to be stored, voltage is applied to the write head • Write head is U-shaped electromagnet, wrapped with windings to flow current in it • B is induced in head when current flows in windings

7. This induced B aligns the domains in disk in the direction of current • This specific direction of field is called magnetic flux • Head induces flux when disk rotates, changing polarity of current change direction of flux called flux reversal or flux transition • A sequence of flux transitions is induced on disk according to stored data • These sequential areas are called bit cells or transition cells

8. Writing process

9. Reading Process • During read process, read head generates a voltage pulse when passes over the flux transition • For positive to negative polarity transition, voltage induces pulse is negative n vice versa • No flux transition generates no pulse • This pulse signal is weak, electronic circuitry amplifies and convert it into original digital data

10. Reading/writing wave forms

11. Geometry of HDD • Geometry of disk can defined by • Tracks • Sectors • Cylinders Data is stored in tracks and sectors • TRACKS • Each disk is broken into concentric circles called tracks, tightly packed circles • Just like annular rings of a tree • SECTORS • A track hold to much information, so it is divided into smaller regions called sectors

12. Sector is the possible smallest unit of storage, usually contain 512 bytes per sector • Old drives contain 17 sectors/track • Newer have thousands of sectors/track, leading to great capacity • CYLINDERS • Each platter has 2 sides to store data • Platters are stacked on top of each other, spin in unison • Identical aligned tracks on each side of every platter together make up a cylinder

13. Tracks and Sectors

14. Cylinders

15. HDD construction • Basic components of HDD are following : • Platters • Recording media • Spindle • Spindle motor • Read/write heads • Sliders and arms • Actuator mechanism • Logic board

16. Parts of HDD

17. Platters • HDD contains one or more disks that hold data, called platters • These are composed of two main parts: substrate material and magnetic media coating • Platters are responsible for data storage so quality of substrate and coating is critical • Normal used platters sizes are : 5 ½ inch, 3 ½ inch, 2 ½ inch and 1 inch • No. of platters vary from 1 to even dozen platters in large server systems

18. Spindle and spindle motor • All platters are physically connected on a common central spindle that spins at one unit driven by spindle motor • Each platter uses both sides for data storage • Platter substrate is to hold the magnetic material, so it should be, rigid, easy to work with, light weight, stable and magnetically inert. • Most commonly used are Aluminum and glass ceramics • Magnetic coating : 1. oxide media (iron oxide) 2. thin film coating

19. HDD and its Platters

20. Read/ write Heads • Interface between the physical data storage medium and electronic component that make up rest of HDD • Convert bits to magnetic pulses, stores on disk and then reverse process when needed • Works on electromagnetism • One head for each side of platter • It does not touch the disk rather floats on air cushion, called floating/flying height or head gap • Head crashes due to dust particles

21. Read/ write heads

22. Head sliders, arms and actuators • Head sliders: RW head is mounted on special device called slider • Have special shapes which allows head to ride on platter • Head arms : triangle in shape on which head sliders are mounted • When arm moves, all heads move as a single assembly • Head Actuators: is the device used to position arms on different tracks on platter surface • very important because reading and writing information from track to track is basic function of HDD

23. Head actuators are of two types • Stepper motors • Voice coils • Stepper Motor. • Electrical motor, move from position to position with click stop positions. If manually spin we can hear click sound at predetermined points • Small (1-3 inches) • Affected by a lot of problems, temperature is main problem • Disk expand and contract track move, stepper can’t move .

24. A stepper motor actuator

25. Voice coil mechanism • Use feedback signal, to accurately position the head on track • Works purely on electromagnetic attraction and repulsion • A coil is wrapped around a metal on the end of head • This assembly is placed near stationary permanent magnet • Current in coil induces B which causes the head to move in one direction or the other depending on attraction and repulsion relative to permanent magnet • By controlling current head motion can controlled

26. A linear Voice Coil actuator

27. References • Alberto Passos Guimaraes Principles of Nanomagnetism NanoScience and Technology 2009 • Alex Hubert, Rudolf Schafer Magnetic Domains The Analysis of Magnetic Microstructures 2008 • www.pcguide.com • Coey, J.M.D. Magnetism and Magnetic Materials 2009

28. Thank you for your patience