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					                  Revision no.: PPT/2K403/02




Hard Disk Drive
                                                                                                                                                                         Revision no.: PPT/2K403/02




Introduction

•   Hard disks allow data to be stored at far denser levels and can
    be accessed very quickly.
•   In a hard disk, the magnetic material is layered on to an
    aluminum or glass platter which is polished to mirror
    smoothness.
•   The information on a hard disk is stored in extremely small
    regions or magnetic domains through the use of control
    mechanisms
•   Control mechanisms arrange magnetic particles in patterns
    that electronically correspond to 0s and 1s.

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Introduction (contd.)

•   In hard disk the head actually 'flies' microns above the surface
    of the platter and is never really allowed to touch the surface of
    the hard disk.
•   In most of the hard disks, the drive platters spin at 5400 RPM,
    7200 RPM, 10000 RPM
•   The arm that controls the head is responsible for moving the
    head to the correct location on the disk
•   Hard disks contain more than one platter, and a corresponding
    number of read-write heads that together decide the capacity
    of the hard disk.
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Introduction (contd.)

•   Many hard disks can store 80GB per platter.

•   This implies that each platter holds 40 GB per side

•   Two read-write heads are used - one for each side of the
    platter.

•   Considering the speeds at which the platters spin, if the heads
    come into contact with the platters, there would be severe
    damage to the disk surface and consequently to the data
    stored.

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Inside of the Hard disk drive.




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The Platter


•   The media is the hard metallic disk made of Aluminum and

    coated with iron oxide which gives a typical rust brown look.

•   Unlike the floppy disk drive, the media in the hard disk drive is

    permanently fixed to the drive mechanism, hence it is also

    called Fixed disk drive.

•   Both sides of the disk platter is coated with the magnetic

    material which provides additional storage space.

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The Platter (contd.)

•   Hard disk surface is formed with concentric circular paths of
    data storage called tracks

•   Each track is sub-divided into sectors

•   The density of tracks on a Hard disk are 300 - 1024 tracks
    (maximum) on one surface

•   where as a floppy disk can have typically 40/80 tracks on one
    surface.

•   The number of sectors/track is also higher than the floppy
    disk, i.e., 17 sectors/tracks against 9 or 15 sectors/tracks.
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The Platter (contd.)

                                The platters and head arrangement
                                      in the hard disk drive.




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Read/Write Head


•   The Hard Disk Drive uses a coil of winding to electrically

    induce magnetic flux on the recording surface or medium.

•   Similar coil is also used to detect the existence of the magnetic

    flux on the medium.

•   These coils form the Write and the Read mechanisms. The

    assembly consisting of the R/W coils is called a head.



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Read/Write Head (contd.)

•   One head assembly is provided for every recording surface

•   The R/W head assembly is mounted on a carriage device

•   It can move linearly to access any of the track spread over the

    entire disk surface.

•   All the heads are mounted on one carriage assembly.

•   This assumes the access of same numbered tracks on all

    surfaces simultaneously i.e., head 0 on surface 0 accesses the

    track 0 (of surface 1) & so on.
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Read/Write Head (contd.)

•   Track 0 of the surface 0,1,2 & 3 in the same plane are called as

    Cylinder 0.

•   When the entire head carriage is moved from a track to access

    another, i.e., from track0 to track1, it is in effect accessing

    cylinder 1.

•   Movement of carriage assembly to move from track to track is

    achieved by driving it with a stepper motor or in some cases a

    voice coil mechanism. This is called head actuation

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Carriage Actuator


•   Carriage actuation in a FDD is done using a stepper motor.

•   Actuation in a HDD which is either done by the stepper motor

    or by the voice coil, depends upon the capacity of the drive.

•   A stepper motor moves in steps rather than continuously.

•   The stepper motor is mechanically linked to the head carriage

    by a split steel band, coiled around the motor spindle.


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Carriage Actuator (contd.)


•   Sometimes the rack and the pinion gear mechanism is also

    used.

•   Usually each step of the motor moves the R/W head by one

    track position.

•   If the head has to move, for example to track number 300, then

    the stepper motor must move 300 steps in the required

    direction.

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Voice coil actuator (contd.)


•   Voice coil method of actuation is done usually in large

    capacity drives.

•   The voice coil mechanism moves the head carriage assembly

    by pure electro-magnetic force.

•   Typically in a hard disk, voice coil is mounted on a track and

    surrounding a stationary magnet.

•   Coil mechanism is connected to the head carriage assembly.


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Voice coil actuator (contd.)

•   As the coil is energized it attracts or repels the stationary
    magnet causing the head carriage to move forward or
    backwards.

•   The tracks on this surface are recorded with index signals to
    represent the cylinders.

•   The head coil on this surface can only detect these index
    signals & they cannot write.

•   This head is called the servo head giving feedback to the servo
    circuitry

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Voice coil actuator (contd.)

•   It determines and controls the position of the head over each
    track thus enabling access to every cylinder on the disk.



    Comparison between Stepper motor and voice coil actuator.
      Function                                                                  Stepper motor                                        Voice coil
      Relative speed                                                            Slow                                                 Fast
      Temperature sensitivity                                                   Yes                                                   No
      Position sensitivity                                                      Yes                                                   No
      Auto head park                                                            No                                                   Yes
      Reliability / Accuracy                                                    Poor                                                 High
      Cost                                                                      Low                                                  High

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Hard Disk Spindle Motor

•   Spindle motor, also sometimes called the spindle shaft, is
    responsible for turning the hard disk platters, allowing the
    hard drive to operate.
•   All PC hard disks use servo-controlled DC spindle motors.
•   Servo system is a closed-loop feedback system which is the
    same technology as is used in modern voice coil actuators.
•   Increasing the speed at which the platters spin improves both
    positioning and transfer performance.
•   Rotational latency is the time that the heads must wait for the
    correct sector number to come under the head.

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Hard Disk Spindle Motor (contd.)

•   Most common PC spindle speeds, their associated average rotational
    latency, and their typical applications are as follows.




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Hard Disk Data Encoding and Decoding

•   Hard disks store information in the form of magnetic pulses.

•   Magnetic information on the disk consists of a stream of (very,
    very small) magnetic fields.

•   Information is stored on the hard disk by encoding information
    into a series of magnetic fields.

•   It is conceptually simple to match "0 and 1" digital information
    to "N-S and S-N" magnetic fields.

•   Earliest encoding methods were relatively primitive and
    wasted a lot of flux reversals on clock information.
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Frequency Modulation (FM)

•   First common encoding system for recording digital data on
    magnetic media was frequency modulation.

•   One is recorded as two consecutive flux reversals, and a zero
    is recorded as a flux reversal followed by no flux reversal.

•   FM is is very wasteful wherein each bit requires two flux
    reversal positions, with a flux reversal being added for
    clocking every bit.

•   FM requires double (or more) the number of reversals for the
    same amount of data.

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Modified Frequency Modulation (MFM)

•   A refinement of the FM encoding method is modified
    frequency modulation, or MFM.
•   MFM improves on FM by reducing the number of flux reversals
    inserted just for the clock.
•   When a 1 is involved there is already a reversal (in the middle
    of the bit) so additional clocking reversals are not needed.
•   When a zero is preceded by a 1, we similarly know there was
    recently a reversal and another is not needed.
•   MFM encoding was used on the earliest hard disks, and also
    on floppy disks.
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Run Length Limited (RLL)

•   Improvement on the MFM encoding technique used in earlier
    hard disks and used on all floppies is run length limited or
    RLL.
•   Two primary parameters define how RLL works, and therefore,
    there are several different variations.
•   RLL considers groups of several bits instead of encoding one
    bit at a time.
•   Two parameters that define RLL are
    – Run length
      It is the minimum spacing between flux reversals
    – Run limit
      It is the maximum spacing between flux reversals.
•   RLL used on a drive is expressed as "RLL (X,Y)" or "X,Y RLL"
    where X is the run length and Y is the run limit.
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Partial Response, Maximum Likelihood (PRML)


•   Traditional method of reading and interpreting hard disk data

    is called peak detection.

•   As data density increases, the flux reversals are packed more

    tightly and the signal becomes much more difficult to analyze

    which can potentially cause bits to be misread from the disk.




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Partial Response, Maximum Likelihood (PRML)
(contd.)




•   It becomes very hard for the circuitry to actually tell where the
    flux reversals are and to combat this problem a new method
    was developed to solve the data interpretation problem and
    this technology, called partial response, maximum likelihood
    or PRML.

•   PRML employs sophisticated digital signal sampling,
    processing and detection algorithms to manipulate the analog
    data stream coming from the disk and then determine the most
    likely sequence of bits this represents.
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Extended PRML (EPRML)

•   Improvement on the PRML design has been developed called
    extended partial response, maximum likelihood, extended
    PRML or just EPRML.

•   EPRML are still based on analyzing the analog data stream
    coming from the read/write head to determine the correct data
    sequence.

•   Use better algorithms and signal-processing circuits to enable
    to accurately interpret the information coming from the disk.


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    Hard Disk Geometry

•    Geometry determines where data is stored on the surface of
     each platter, and maximum storage capacity of the drive.
•    There are five numerical values that describe geometry:
     – Heads
     – Cylinders
     – Sectors per track
     – Write precompensation
     – Landing zone
•    Note:- All hard disk drives have geometry factors that must be
     known by the BIOS to read and write to the drive.

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Heads

•   The number of heads is relative to the total number of sides of
    all the platters used to store data.
•   The maximum number of heads limited by BIOS is 16.
•   Some hard disk drive manufacturers use a technology called
    sector translation.
•   This allows some hard drives to have more than two heads per
    platter.
•   It is possible for a drive to have up to 12 heads but only one
    platter. Max 16

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Heads (contd.)




                                                                        Drive heads




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Cylinders

•   Data is stored in circular paths on the surface of each platter.
    Each path is called a track.

•   A set of tracks (all of the same diameter) in each platter is
    called a cylinder.

•   Number of tracks per surface is identical to the number of
    cylinders.

•   The number of cylinders is a measurement of drive geometry;
    the number of tracks is not a measurement of drive geometry.
    BIOS limitations set the maximum number of cylinders at 1024.

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Cylinders (contd.)

                                                                                  Cylinders




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Sectors per Track

•   A hard disk drive is cut (figuratively) into tens of thousands of
    small arcs, like a pie. Each arc is called a sector and holds 512
    bytes of data
•    BIOS limitations set the maximum number of sectors per track
    at 63.




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Write Precompensation Cylinder

•   Older hard drives had a real problem with the fact that sectors

    towards the inside of the drives were much smaller than

    sectors toward the outside.

•   An older drive would write data a little further apart once it got

    to a particular cylinder and this cylinder was called the Write

    Precompensation (write precomp) cylinder.

•   Hard drives no longer have this problem, making the write

    precomp setting obsolete.

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Landing Zone

•   Old stepper motor hard drives needed to have the read/write
    heads parked before being moved in order to avoid accidental
    damage.

•   Landing zone value designated an unused cylinder as a
    "parking place" for the read/write heads.

•   Today's voice coil drives park themselves whenever they're
    not accessing data, automatically placing the read/write heads
    on the landing zone.


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Interleaving


•   Platters of the hard drive are rotating with a very high speed;

    typically 3600 rpm and above

•   While recording the data one or two sectors may skip till the

    write signal is received, if they are numbered one after the

    other.

•   If this happens a second sector will be read after completing a

    full rotation and the speed of the hard disk will slow down

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Interleaving (contd.)


•   To avoid this problem the sectors are numbered separating

    them physically from each other.

•   This process is named as INTERLEAVING PROCESS

•   The factor by which it is separated is known as INTERLEAVE

    FACTOR.

•   INTERLEAVE RATIO is the ratio by which the sectors are

    separated from each other.


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Interleaving (contd.)

•   For IDE drives generally the interleave (optimum value) is 1,
•   Due to the integrated logic the IDE drives use 1:1 interleave
    ratio


Note
•   Due to advance BIOS chipset we can implement 1:3 or more
    for IDE interface hard disk.
•   This can be done even by the utility called as DM (Disk
    Manager).

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Interleaving (contd.)

•   Interleave ratio 1:1,1:2,1:3 was used in IDE, ESDI, SCSI
    respectively




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Physical Geometry

•   Physical geometry of a hard disk is the actual physical number
    of heads, cylinders and sectors used by the disk.
•   Original setup parameters in the system BIOS are designed to
    support the geometries of these older drives.
•   There are three figures that describe the geometry of a drive:
    the number of cylinders on the drive ("C"), the number of
    heads on the drive ("H") and the number of sectors per track
    ("S") and together they comprise the "CHS" method of
    addressing the hard disk.
•   Today's drives do not have simple geometries and therefore
    do not have the same number of sectors for each track, and as
    a result drives must be accessed using logical geometry
    figures, with the physical geometry hidden behind routines
    inside the drive controller.
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Logical Geometry

•   When you perform a drive parameter autodetection in your
    system BIOS setup or look in your new IDE/ATA hard disk's
    setup manual, you are seeing the logical geometry values that
    the hard disk manufacturer has specified for the drive.

•   Since newer drives use zoned bit recording it is not possible to
    set up the disk in the BIOS using the physical geometry.

•   BIOS routines for the original AT command set allowed a hard
    drive size only upto 504 MB wherein a drive could have no
    more than 1024 cylinders, 16 heads, and 63 sectors/track.

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Logical Geometry (contd.)

•   Older hard disks that had simple structures and low capacity
    did not need special logical geometry.

•   Newer drives cannot have their true geometries expressed
    using three simple numbers and thus BIOS is given bogus
    parameters that give the approximate capacity of the disk, and
    hard disk controller is given intelligence so that it can do
    automatic translation between the logical and physical
    geometry.


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LBA (Logical Block Addressing)

•   Most modern drives can be accessed using logical block
    addressing (LBA) instead of using the logical geometry
    numbers directly.
•   In this method a totally different form of logical "geometry" is
    used wherein the sectors are just given a numerical sequence
    starting with 0 and the drive just internally translates these
    sequential numbers into physical sector locations.
•   Largest logical geometry numbers for IDE/ATA drives are
    16,383 cylinders, 16 heads and 63 sectors which yields a
    maximum capacity of 8.4 GB.
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INT13 Extensions

•   In 1994, Phoenix Technologies (the BIOS manufacturer) came
    up with a new set of BIOS commands called Interrupt 13
    extensions (INT13) by feeding the LBA a stream of
    "addressable sectors".
•   Drives larger than 8.4 GB can no longer be accessed using
    regular BIOS routines, and require extended Int 13h
    capabilities.
•   System with INT13 extensions can handle drives upto 137GB.
•   Hard drives must be accessed directly by an operating system
    supporting Int 13h BIOS extensions to see the whole drive, or
    drive overlay software used and if the drive is addressed using
    conventional geometry parameters, it will be limited in capacity
    to only 8.4 GB.
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Hard-Drive Types

•   When IBM created the first CMOS on the 286 AT, they believed
    that the five different geometry numbers would be too
    complicated for normal users to configure and thus IBM
    established 15 present combinations of hard-drive geometries,
    called hard-drive types.
•   Initially, it worked well, a problem arose for larger capacity
    hard drives and thus IBM expanded the list to 37 different
    types.
•   IBM later topped using drives that required unique geometries
    and stopped adding drive types.
•   American Megatrends(AMI) created a new "user" type whereby
    instead of selecting a special type, users could enter in the five
    geometry values manually which provided more flexibility for
    hard-drive installation.
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Autodetection

•   Manual installation process was always a bit of a problem.

•   Today, all PCs can set the CMOS properly by using

    autodetection.

•   Autodetection simply means that the CMOS asks the drive for

    those stored values and automatically updates the CMOS.

•   Most CMOS setup utilities have a hard-drive type called "Auto“

    and by setting the hard-drive type to Auto, the CMOS

    automatically updates itself every time the computer is started.

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Hard Disk Interfaces and Configuration

•   The interface is the communication channel over which all the
    data flows that is read from or written to the hard disk.

•   Nowadays there are really only two main interfaces used for
    hard disks: IDE/ATA and its variants, and SCSI and its
    variants.

•   Presence of IDE/ATA controllers on all modern motherboards
    makes this interface less expensive for most people than
    going with SCSI, which would require the addition of a SCSI
    host adapter.

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ST-506 / ST-412 Interface

•   Developed in 1980 by Seagate Technologies, to work with the
    company's 5 MB ST-506 hard disk and later revised to support
    the 10 MB ST-412.

•   In hard disks of these type, there was no built in logic board as
    modern drives have.

•   This interface is recognized in older systems by the use of two
    ribbon cables wherein one of the cables is 20 pins wide and
    carries data, and the other is 34 pins and carries control
    signals.
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Enhanced Small Device Interface (ESDI)


•   ESDI was developed in the mid-1980s by a consortium of hard

    disk manufacturers led by Maxtor.


•   It had a maximum theoretical bandwidth of 24 Mbits/second.


•   ESDI suffered under competition from IDE/ATA which offered

    simpler configuration, lower cost and improved performance.



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Integrated Drive Electronics / AT
Attachment (IDE/ATA) Interface

•   Most popular interface used in modern hard disks, commonly
    known as IDE.
•   IDE drives were the first ones to popularize integrating the
    logic controller onto the hard disk itself.
•   First hard disks to have integrated controllers weren't
    technically using the IDE/ATA interface but were in fact so-
    called "hardcards", which were designed and sold by the "Plus
    Development" division of Quantum.
•   Connection to the system bus was maintained through the use
    of a cable that ran either directly to a system bus slot, or to a
    small interfacing card that plugged into a system bus slot.

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Integrated Drive Electronics / AT
Attachment (IDE/ATA) Interface (contd.)

•   Later, chipset manufacturers began integrating IDE/ATA hard
    disk controllers into their chipsets, so that instead of
    connecting the drives to a controller card, they were
    connected directly to the motherboard.
•   Connection between the system and the hard disks is 16 bits
    wide, so two bytes of data are passed at a time between the
    system and any hard disk.
•   Two drives are supported on each IDE/ATA channel, with
    special signalling used to ensure that commands sent for one
    drive don't interfere with the other.
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Integrated Drive Electronics / AT
Attachment (IDE/ATA) Interface (contd.)


•   First formal standard defining the AT Attachment interface was

    submitted to ANSI for approval in 1990.

•   Western Digital, created "Enhanced IDE" or "EIDE", a

    somewhat different ATA feature set expansion which included

    powerful features such as higher capacities, support of non-

    hard drive storage devices, for a maximum of four ATA

    devices and substantially improved throughput.

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IDE Interface

                                                            IDE connections




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SFF-8020 / ATA Packet Interface (ATAPI)

•   IDE/ATA interface, originally was designed to work only with
    hard disks.

•   A special protocol was developed called the AT Attachment
    Packet Interface or ATAPI which is used for devices like
    optical, tape and removable storage drives.

•   It enables CDROMs etc. to plug into the standard IDE cable
    used by IDE/ATA hard disks, and be configured as master or
    slave, etc. just like a hard disk would be.


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SFF-8020 / ATA Packet Interface (ATAPI) (contd.)


•   ATAPI driver is used to communicate with ATAPI devices

    which must be loaded into memory before the device can be

    accessed.

•   ATAPI devices will coexist with IDE/ATA devices and behave

    as if they are regular IDE/ATA hard disks and will even allow

    booting from it.



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Small Computer Systems Interface (SCSI)


•   Small Computer Systems Interface, abbreviated SCSI and

    pronounced "skuzzy". is a much more advanced interface than

    IDE/ATA, and is preferable for many situations, usually in

    higher-end machines.

•   It is less commonly used due to its higher cost and the fact

    that its advantages are not useful for the typical home or

    business desktop user.


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SATA Interface

•   New high-speed serial interface
    for mass storage that will
    eventually replace Parallel ATA
    (PATA), the current mass storage
    attachment standard.

•   Advantages of increased
    bandwidth 150-300 Mb/s as
    compared to 100 Mb/s for PATA,
    thinner, longer cables, lower
    voltages and no jumpers.

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IDE/ATA Transfer Modes and Protocols


•   Most of the advances in newer IDE/ATA standards are oriented

    around creating faster ways of moving data between the hard

    disk and the PC system.


•   IDE/ATA interface is a communication channel, requiring

    support from the devices on both ends of the channel.




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Programmed I/O (PIO) Modes


•   Oldest method of transferring data over the IDE/ATA interface


    is through the use of programmed I/O.


•   There are several different speeds of programmed I/O, called


    programmed I/O modes, or more commonly, PIO modes.




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Programmed I/O (PIO) Modes (contd.)

•   Table below shows the five different PIO modes




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Direct Memory Access (DMA) Modes and
Bus Mastering DMA

•   PIO method requires a fair bit of overhead, as well as the care
    and attention of the system's CPU.

•   Direct memory access or DMA is the generic term used to refer
    to a transfer protocol where a peripheral device transfers
    information directly to or from memory, without the system
    processor being required to perform the transaction.

•   There are two different ways of doing DMA transfers:
    – Conventional DMA / Third party DMA

    – Bus Mastering DMA / First party DMA

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Direct Memory Access (DMA) Modes
and Bus Mastering DMA (contd.)

•   Conventional DMA / Third party DMA
    In this method the DMA controllers on the motherboard
    coordinate the DMA transfers.

•   Bus Mastering DMA / First party DMA
    In this method the peripheral device itself does the work of
    transferring data to and from memory, with no external DMA
    controller involved which is also called bus mastering because
    when such transfers are occurring the device becomes the
    "master of the bus".
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Ultra DMA (UDMA) Modes

•   In Ultra DMA, data is transferred on both the rising and falling

    edges of the clock.

•   Double transition clocking, along with some other minor

    changes made to the signalling technique to improve

    efficiency, allowed the data throughput of the interface to be

    doubled for any given clock speed.

•   First implementation included three Ultra DMA modes,

    providing up to 33 MB/s of throughput.

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Ultra DMA (UDMA) Modes (contd.)

•   Table below shows all of the current Ultra DMA modes, along
    with their cycle times and maximum transfer rates:




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IDE/ATA Controllers

•   A device that resides within the system and interfaces with a
    peripheral device is often commonly called a "controller“
•   IDE/ATA controller acts as the middleman between the hard
    disk's internal controller and the rest of the system.
•   Data pathway over which information flows in the IDE/ATA
    interface is called a channel.
•   Each IDE channel is capable of communicating with up to two
    IDE/ATA devices however theoretically it is possible to
    configure and use as many as four (or even more) different
    IDE/ATA interface channels on a modern PC.

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Single, Master and Slave Drives and Jumpering


•   It is necessary to have some way of differentiating between the

    two devices on the same channel which is done by giving each

    device a designation as either master or slave, and then

    having the controller address commands and data to either

    one or the other.

•   Devices are designated as master or slave using jumpers,

    small connectors that fit over pairs of pins to program the

    drive through hardware.

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IDE/EIDE Identification


                                      Master and slave jumper settings




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Hard Disk Logical Structures and File Systems


•   File system is the general name given to the logical structures

    and software routines used to control access to the storage on

    a hard disk system.

•   Operating systems use different ways of organizing and

    controlling access to data on the hard disk, and this choice is

    basically independent of the specific hardware being used-the

    same hard disk can be arranged in many different ways, and

    even multiple ways in different areas of the same disk.
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PC File Systems


•   There are many different types of file systems in use by

    different operating systems for PC hardware which are as

    follows:

    – FAT16

    – Virtual FAT (VFAT)

    – FAT32 (32-bit FAT)

    – NTFS


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File Allocation Table File System (FAT,
FAT12, FAT16)

•   It is the file system that was used by DOS on the first IBM PCs,
    and it became the standard for the PCs that followed.
•   FAT in Concept
    – Base storage area for hard drives is a sector, with each sector
        storing upto 512 bytes of data.
    – MS-DOS version 2.1 first supported hard drives using a special
        data structure to keep track of stored data on the hard drive, and
        Microsoft called this structure the FAT.
    – FAT is a data structure but it is more like a two-column
        spreadsheet.

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File Allocation Table File System (FAT,
FAT12, FAT16) (contd.)

  – Left column gives each sector a number, from 0000 to FFFF which
     means there are 65,536 (64K) sectors and thus this type of FAT is
     called a "16-bit FAT".
  – Right-hand side of the FAT contains information on the status of
     sectors.
  – 16-bit FAT addresses a maximum of 64K (216) locations and
     therefore, the size of a hard-drive partition should be limited to
     64K x 512 bytes per sector, or 32MB.
  – One needed an improvement to the 16-bit FAT, a new and
     improved FAT16 that would enable larger drives which led to the
     development of a dramatic improvement in FAT16, called
     clustering.
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File Allocation Table File System (FAT,
FAT12, FAT16) (contd.)


  – Clustering simply means to combine a set of contiguous sectors

     and treat them as a single unit in the FAT and these units are

     called file allocation units or clusters.


  – FAT16 could support partitions up to 2GB since FAT 16 still only

     contained 64K storage areas.




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File Allocation Table File System (FAT,
FAT12, FAT16) (contd.)

•   Table shows the number of sectors per cluster for FAT16.




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Virtual FAT (VFAT)

•   When Microsoft introduced Windows 95 in,1995, a new
    variation of FAT was introduced called Virtual FAT or VFAT for
    short.
•   VFAT has several key features and improvements compared to
    FAT16 which are
    – Long File Name Support
    – Improved Performance
    – Better Management Capabilities

•   Only significant change in terms of actual structures is the
    addition of long file names.
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FAT32 (32-bit FAT)

•   Hard disk manufacturers started to create drives so large that
    FAT16 could not be used to format a whole drive in a single
    partition thus to correct this situation, Microsoft created
    FAT32.
•   FAT32 uses 32-bit numbers to represent clusters, instead of
    the 16-bit numbers used by FAT16.
•   It allows single partitions of very large size to be created,
    where FAT16 was limited to partitions of about 2 GB and
    supports partitions up to 2 terabytes.
•   FAT32 was first introduced in Windows 95's OEM Service
    Release2 was later included in Windows 98, Windows ME and
    Windows 2000, and Windows 2003 as well.
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New Technology File System (NTFS)

•   One of the key elements of Windows NT's architecture was the
    file system created especially for the operating system, called
    the New Technology File System or NTFS.

•   It includes many features, including file-by-file compression,
    full permission control and attribute settings, support for very
    large files, transaction-based operation as well as
    performance-enhancing features such as RAID support.

•   Significant drawbacks are increased complexity, and less
    compatibility with other operating systems compared to FAT.
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Master Boot Record (MBR)


•   Every hard disk must have a consistent "starting point" where

    key information is stored about the disk, such as how many

    partitions it has, what sort of partitions they are, etc.

•   Place where this information is stored is called the master boot

    record (MBR) which is always located at cylinder 0, head 0, and

    sector 1, the first sector on the disk.


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Master Boot Record (MBR) (contd.)


•   Master boot record contains the following structures:

    – Master Partition Table

        This small table contains the descriptions of the partitions that are

        contained on the hard disk.

    – Master Boot Code

        The master boot record contains the small initial boot program

        that the BIOS loads and executes to start the boot process.




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Partition Types

•   A hard drive may have up to four partitions. These partitions

    divide into one of two types: primary and extended.

•   Primary Partitions

    – Primary partitions store the OS(s) and if you want to boot from a

        hard drive, it must have a primary partition.

    – In Windows 9x and 2000, the primary partition is always C:, and

        you cannot change.

    – A hard drive can have up to four primary partitions.


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Active Partition


•   Active partition comes into play when a hard drive stores

    multiple primary partitions, each with a valid operating system.

•   For a primary partition to boot, you must set it as the active

    partition.

•   MBR looks for a primary partition set to "active".




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Boot Managers


•   Programs specifically designed for the task of booting and

    they are usually called Boot Managers or boot loaders.

•   It analyzes the primary partitions on the disk and then presents

    a menu to you and asks which operating system you want to

    use.

•   Boot managers are in many ways indispensable when working

    with multiple operating systems.


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Extended Partition

•   Extended partitions are not bootable and one hard drive can
    only have one extended partition.

•   Extended partitions are completely optional.

•   When you create an extended partition, it does not
    automatically get a drive letter instead, you divide the
    extended partition into "logical drives".

•   An extended partition may have as many logical drives as you
    wish, limited only by the letters of the alphabet for Windows 9x
    systems.

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Partitioning

•   Partitioning the hard disk is the act of dividing it into pieces.
•   Partitions are one of the major disk structures that define how
    the disk is laid out.
•   Rules that govern partition setup are as follows:
     – A maximum of four primary partitions can be placed on any hard
        disk.
     – Only one partition may be designated, at any given time, as active.
     – DOS will only recognize the active primary partition.
     – One of the four partitions may be designated as an extended DOS
        partition.
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Fdisk startup screen




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Troubleshooting Tips

•   Some of the tips are as follows:
    – If your computer won't boot from your hard drive
            • Run FDISK again and check whether the partition is set to active.
    – If FDISK reports a disk size that isn't true
            • BIOS may be incorrectly identifying your hard drive and thus run your
                  BIOS setup program and confirm the size.
    – No access to a particular hard disk.
            • Simply boot from your Windows CD and let the SETUP program
                  format the disk for you or
            • If you've started the PC with a startup floppy made with Windows
                  95/98, use the /S switch with the FORMAT command (FORMAT C: /S)
                  to copy the system files.

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Exercise

•   Exercise 18.1        Identification and Simple troubleshooting
•   Exercise 18.2 Partitioning using Fdisk and Formatting the Hard
    disk
•   Exercise 18.3 Using PQ Magic on a Hard Disk
•   Exercise 18.4 Backing Up and Restoring the MBR of the Hard
    disk
•   Exercise 18.5 Using Norton Ghost for Imaging of a Hard disk




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