CDROM, Floppy and Hard Disk Structure

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CDROM, Floppy and Hard Disk Structure
Plus some basic concepts
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Table of Contents

• CD
• History
• Structure
• Data Recording
• How The CD Drive Works
• CD File Systems
• Multiple Sessions
• CD-ReWritable (CD-RW)
• DVD

• Floppy Disk
• History
• Structure
• Data Recording/Retrieval
• Formatting
• 3½ Inch (2HD) Disks
• Hard Disk
• Some Basic Concepts
• Boot Sector
• Cluster
• FAT
• NTFS

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PART 1

• CD-ROM

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History

• Compact Disc - Digital Audio (CD-DA), the
  original CD specification developed by Philips
  and Sony in 1980
• Specifications were published in Red Book,
  continued to be updated (lastest version in 1999)
• In 1985 a standard for the storage of computer
  data by Sony and Philips, CD-ROM (Compact Disc
  Read Only Memory)
• Developments in the technology have been ongoing
  and rapid
• Compact disc Interactive (CD-I)
• Compact Disc Television (CD-TV)
• Compact Disc Recording (CD-R)
• Digital Video Disc (DVD)

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Structure

• The thickness of a CD can vary between 1.1 and
  1.5mm
• CDROM can store 720 MB of data.
• A CD consists of four layers

• The biggest part is clear polycarbonate
  (nominally 1.2mm)
• There is a very thin layer of reflective metal
  (usually aluminum) on top of the polycarbonate
• Then a thin layer of some protective material
  covering the reflective metal
• A label or some screened lettering on top of
  protective material

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CD Layers (contd)
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Structure

• A CDROM Drive uses a small plastic-encapsulated
  disk that can store data
• This information is retrieved using a Laser Beam
• A CD can store vast amounts of information
  because it uses light to record data in a tightly
  packed form

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Structure (contd)

• On surface of CDROM, laser beam to use to was be
  "punched" to according the spiral called the
  pits. These positions do not have "punch" as
  land.
• The 0.12 micron deep pit, approximately 0.6
  microns wide.
• The pit and land length from 0.9 to 3.3 microns.
• The distance between the spiral is 1.6 micron.
• Track density on a CDROM is about 16,000 tracks
  per inch.

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CD Safety

• The label side of a CD is the most vulnerable
  part of the disk
• The other side is protected by the thick (1.2mm)
  and hard polycarbonate
• It is possible to carefully clean and even to
  polish this surface to remove fingerprints and
  even scratches
• Many flaws on the polycarbonate surface will
  simply go unread.

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CD vs. Magnetic Media

• In Magnetic Media (like floppy/hard disk) the
  surface is arranged into concentric circles
  called tracks
• Number of sectors per track is constant for all
  tracks
• The CD has one single track, starts at the center
  of the disk and spirals out to the circumference
  of the disk
• This track is divided into sectors of equal size

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CD Data Recording

• Information is recorded on a CD using a series of
  bumps

• In the recording, Lazer gun was used to write
  data to disk
• Signal corresponding to 0 gt laser off.
• Signal corresponding to 1 gt laser on gt burned
  disk surface into a point of losing the ability
  to reflect

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Data Recording (contd)

• The unmarked areas between pits are called
  "lands
• Lands are flat surface areas

• The information is stored permanently as pits and
  lands on the CD-ROM. It cannot be changed once
  the CD-ROM is mastered, this is why its called
  CD-ROM

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Data Reading

• Laser reflection on rotating disk surface, the
  pit will be lost reflected rays gt that is 0
  signal, the land they received reflected rays gt
  that is 1 signal

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How The CD Drive Works

• A motor rotates the CD
• The rotational speed varies so as to maintain a
  constant linear velocity (the disk is rotated
  faster when its inner "SPIRALS" are being read)

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How The CD Drive Works (contd)

• A laser beam is shone onto the surface of the
  disk
• The light is scattered by the pits and reflected
  by the lands, these two variations encode the
  binary 0's and 1's
• A light sensitive diode picks up the reflected
  laser light and converts the light to digital
  data

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How The CD Drive Works (contd)
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CD-ROM Drive Speed

• The CD-ROM drives are classified by their
  rotational speed
• Based on the original speed of a CD-Audio (e.g. A
  "2X" CD-ROM drive will run at twice the speed of
  a CD- Audio)

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CD Physical Specifications
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CD File Systems

• 1. ISO-9660
• The base standard defines three levels of
  compliance
• Level 1 limits file names to 83 format. Many
  special characters (space, hyphen, equals, and
  plus) are forbidden
• Level 2 and 3 allow longer filenames (up to 31)
  and deeper directory structures (32 levels
  instead of 8)
• Level 2 and 3 are not usable on some systems,
  special MS-DOS

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CD File Systems (contd)

• 2. Rock Ridge
• Extensions to ISO-9660 file system
• Favored in the Unix world
• Lifts file name restrictions, but also allows
  Unix-style permissions and special files to be
  stored on the CD
• Machines that don't support Rock Ridge can still
  read the files because it's still an ISO-9660
  file system (they won't see the long forms of the
  names)
• UNIX systems and the Mac support Rock Ridge
• DOS and Windows currently don't support it

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CD File Systems (contd)

• 3. Joliet
• Favored in the MS Windows world
• Allows Unicode characters to be used for all text
  fields (including file names and the volume name)
• Disk is readable as ISO-9660, but shows the long
  filenames under MS Windows
• HFS (Hierarchical File System)
• Used by the Macintosh in place of the ISO-9660,
  making the disk unusable on systems that don't
  support HFS

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Multiple Sessions

• Allows CDs to be written more than once (not
  re-written)
• Some CD writers support this feature
• About 640MB of data can be written to the CD, as
  some space is reserved for timing and other
  information
• Each session written has an overhead of
  approximately 20MB per session

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CD-ReWritable (CD-RW)

• It is essentially CD-R
• Allows discs to be written and re-written up to
  1000 times
• The storage capacity is the same as that for CD-R
• Based on phase-change technology.
• The recording layer is a mixture of silver,
  indium, antimony and tellurium

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CD-RW Recording Process

• The recording layer is polycrystalline
• The laser heats selected areas of the recording
  track to the recording layer's melting point of
  500 to 700 degrees Celsius

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CD-RW Recording (contd)

• The laser beam melts the crystals and makes them
  non-crystalline (amorphous phase)
• The medium quickly cools, locking in the
  properties of the heated areas
• The amorphous areas have a lower reflectivity
  than the crystalline areas
• This creates a pattern which can be read as pits
  and lands of the traditional CD
• To erase a CD-RW disc, the recording laser turns
  the amorphous areas back into crystalline areas

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DVD

• Digital Versatile Disk (Formerly Digital Video
  Disk)

• Same size (120mm) and thickness (1.2mm) as CD
• Improvements in the logarithms used for error
  correction
• Much greater data accuracy using smaller Error
  Correction Codes (ECC)
• More effective use of the track space

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DVD vs. CD

• DVD uses a tighter spiral (track or helix) with
  only 0.74 microns between the tracks (1.6 microns
  on CDs)
• DVD recorders use a laser with a smaller
  wavelength, 635nm or 650 nm (visible red light)
  vs. 780nm (infrared) for CDs
• DVD has smaller "burns" (pits) in the translucent
  dye layer (0.4 microns minimum vs. 0.83 microns
  minimum on CDs)

• These technologies allow DVDs to store large
  amounts of data

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DVD (contd)

• Standard single-sided DVDs store up to 4.7GB of
  data
• Dual-sided discs hold about 8.5GB of data (9.4GB
  for back-to-back layers dual-sided discs)
• In back-to-back layers discs, it must be turned
  over to access the data on the reverse side
• DVD uses MPEG2 compression for high quality
  pictures
• DVD drives have a much faster transfer rate than
  CD drives
• DVD-ROM drives will read and play existing CD-ROM
  and CD-A disks

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DVD (contd)
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PART 2

• Blu-ray VS HD-DVD

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Blu-ray disc

• Blu-ray Disc (official abbreviation BD) is an
  optical disc storage medium designed to replace
  the DVD format.
• The standard physical medium is a 12 cm plastic
  optical disc, the same size as DVDs and CDs.
• Blu-Ray Discs contain 25 GB per layer, with dual
  layer discs (50 GB) the norm for feature-length
  video discs and additional layers possible later.

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HD - DVD

• HD DVD-ROM, HD DVD-R and HD DVD-RW have a
  single-layer capacity of 15 GB, and a dual-layer
  capacity of 30 GB.
• HD DVD-RAM has a single-layer capacity of 20 GB.
  Like the original DVD format, the data layer of
  an HD DVD is 0.6 mm below the surface to
  physically protect the data layer from damage.
• All HD DVD players are backward compatible with
  DVD and CD.

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USB Flashdrive

• A USB flash drive consists of a flash memory data
  storage device integrated with a USB (Universal
  Serial Bus) interface.
• USB flash drives are typically removable and
  rewritable, and physically much smaller than a
  floppy disk.
• Most weigh less than 30 gram. Storage capacities
  in 2010 can be as large as 256 GB with steady
  improvements in size and price per capacity
  expected.

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USB speed

• USB 1.0 speed 1.5 Mb/s
• USB 1.1 speed 12 Mb/s
• USB 2.0 speed 480 Mb/s
• USB 3.0 speed 5 Gb/s

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Hard disk drive

• Disk platter
• Read/Write head
• Head arm/Head slider
• Head actuator mechanism
• Spindle motor
• Logic board
• Air filter
• Cables Connectors

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Hard Disk

• Fixed and removable
• Fast (disk rotates at 60 to 200 times per second)

• Currently 20 2 TB (may be limited by the
  version of the operating system)
• Like floppies, uses the magnetic properties of
  the coating material, but the technology is
  different

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Boot Sector (Boot Record)

• A vital sector, disk will be unusable if this
  sector damages
• MBR at CHS 0, 0, 1 in hard disks, contains
  Partition Table
• Each partition has its own boot sector too
• Each operating system has its own boot sector
  format
• For Booting, Bootstrap Loader loads Boot Sector
  data it in a particular address of memory
  (00007C00h) and sets the PC
• In hard disks, the small program in MBR attempts
  to locate an active (bootable) partition in
  partition table
• If found, the boot record of that partition is
  read into memory (location 00007C00) and runs

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DOS/Win Formatted Disk

• A DOS/Win formatted floppy/hard disks Boot
  Sector contains
• A jump and a NOP (No Operation Performed) op-code
  (operation code)
• BPB (BIOS Parameter Block)
• Sectors per cluster
• Number of Root directory entries
• Sectors per FAT
• Volume Label
• A program, to load OS if bootable/show error msg
  if not in floppies, to locate the active
  partition in hard disks
• Error messages

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Cluster

• Data units of disk must be addressed, which units
  belong to which file / are free / are damaged
  (bad sectors) /
• On disks having large capacity, purposing one
  sector as a unit makes addressing table so large
  ? Cluster is defined
• Represents the smallest amount of disk space that
  OS can be allocated
• The smaller the cluster size, the more
  efficiently disk space usage, the more number of
  bits to address one unit
• The number of sectors per cluster is stored in
  the
• Boot Record

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FAT

• FAT-12/FAT-16/FAT-32 are Microsoft favorite File
  Allocation Tables (before NTFS)
• FAT-12 uses 12 bits for addressing, a max. of
  4096 units, considering one sector as a cluster,
  2MB can be addressed
• FAT-16 with max.(128) sectors/cluster (64KB
  cluster size ? wasting large amount of disk
  space) up to 4GB, this is why Win95 cannot
  support more than 4GB partiotions
• FAT-32, the same system,
• 32 bit fields for addressing

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NTFS

• NT File System
• Better performance
• Less wasted space
• More security
• Supports all sizes of clusters (512b - 64 KB)

• The 4 KB cluster is somehow standard
• Practically no partition size limitation
• Very flexible, all the system files can be
  relocated, except the first 16 MFT (Master File
  Table) elements

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NTFS (contd)

• NTFS disk is symbolically divided into two parts
• The first 12 is assigned to MFT area
• The rest 88 represents usual space for files
  storage
• MFT area can simply reduce if needed, clearing
  the space for recording files
• At clearing the usual area, MFT can be extended
  again

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Hard Drive Interfaces

• ATA interfaces dominate todays market
• Many changes throughout years
• Parallel ATA (PATA) historically prominent
• Serial ATA (SATA) since 2003
• Small Computer System Interface (SCSI)
• Pronounced Scuzzy
• Used in many high-end systems

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ATA Overview
IDE - International Development Enterprises
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ATA-1

• Programmable I/O (PIO)traditional data transfer
• 3.3 MBps to 8.3 MBps
• DMAdirect memory access
• 2.1 MBps to 8.3 MBps
• Allowed two drives (one master, one slave)

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ATA-2

• Commonly called EIDE (though a misnomer)
• Added second controller to allow for four drives
  instead of only two
• Increased size to 8.2 GB
• Added ATAPI
• Could now use CD drives

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ATA-3

• Self-Monitoring Analysis and Reporting Technology
• S.M.A.R.T.
• No real change in other stats

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ATA-4

• Introduced Ultra DMA Modes
• Ultra DMA Mode 0 16.7 MBps
• Ultra DMA Mode 1 25 MBps
• Ultra DMA Mode 2 33 MBps
• Ultra DMA Mode 2 also called ATA/33

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INT13-Interrupt Extensions

• ATA-1 standard actually written for hard drives
  up to 137 GB
• BIOS limited it to 504 MB due to cylinder, head,
  and sector maximums
• ATA-2 implemented LBA (Logical block addressing)
  to fool the BIOS, allowing drives to be as big as
  8.4 GB
• INT13 Extensions extended BIOS commands
• Allowed drives as large as 137 GB

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ATA-5

• Introduced newer Ultra DMA Modes
• Ultra DMA Mode 3 44.4 MBps
• Ultra DMA Mode 4 66.6 MBps
• Ultra DMA Mode 4 also called ATA/66
• Used 40-pin cable, but had 80 wires
• Blue connectorto controller
• Gray connectorslave drive
• Black connectormaster drive

ATA/66 cable
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ATA-6

• Big Drives introduced
• Replaced INT13 24-bit LBA to 48-bit LBA
• Increased maximum size to 144 PB
• 144,000,000 GB
• Introduced Ultra DMA 5
• Ultra DMA Mode 5 100 MBps ATA/100
• Used same 40-pin, 80-wire cables as ATA-5

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ATA-7

• Introduced Ultra DMA 6
• Ultra DMA Mode 6 133 MBps ATA/133
• Used same 40-pin, 80-wire cables as ATA-5
• Didnt really take off due to SATAs popularity
• Introduced Serial ATA (SATA)
• Increased throughput to 150 MBps to 300 MBps

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Serial ATA

• Serial ATA (SATA) creates a point-to-point
  connection between the device and the controller
• Hot-swappable
• Can have as many as eight SATA devices
• Thinner cables resulting in better airflow and
  cable control in the PC
• Maximum cable length of 39.4 inches compared to
  18 inches for PATA cables

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Serial ATA

• More on SATA
• PATA device my be connected to SATA using a SATA
  bridge
• Can have as many as eight SATA devices
• Add more SATA functionality via a PCI card
• eSATA
• External SATA
• Extends SATA bus to external devices

eSATA Port
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SCSISmall Computer System Interface

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SCSI

• Pronounced Scuzzy
• Been around since 70s
• Devices can be internal or external
• Historically the choice for RAID
• Faster than PATA
• Could have more than four drives
• SATA replacing SCSI in many applications

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SCSI Chains

• A SCSI chain is a series of SCSI devices working
  together through a host adapter
• The host adapter is a device that attaches the
  SCSI chain to the PC
• All SCSI devices are divided into internal and
  external groups
• The maximum number of devices, including the host
  adapter, is 16

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Internal Devices

• Internal SCSI devices are installed inside the PC
  and connect to the host adapter through the
  internal connector
• Internal devices use a 68-pin ribbon cable
• Cables can be connected to multiple devices

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External Devices

• External SCSI devices are connected to host
  adapter to external connection of host adapter
• External devices have two connections in the
  back, to allow for daisy-chaining
• A standard SCSI chain can connect 15 devices,
  including the host adapter

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SCSI IDs

• Each SCSI device must have a unique SCSI ID
• The values of ID numbers range from 0 to 15
• No two devices connected to a single host adapter
  can share the same ID number
• No order for the use of SCSI IDs, and any SCSI
  device can have any SCSI ID

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SCSI IDs

• The SCSI ID for a particular device can be set by
  configuring jumpers, switches, or even dials
• Use your hexadecimal knowledge to set the device
  ID
• Device 1 0 0 0 1 Off, Off, Off, On
• Device 7 0 1 1 1 Off, On, On, On
• Device 15 1 1 1 1 On, On, On, On
• Host adapters often set to 7 or 15 but can be
  changed

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Termination

• Terminators are used to prevent a signal
  reflection that can corrupt the signal
• Pull-down resistors are usually used as
  terminators
• Only the ends of the SCSI chains need to be
  terminated
• Most manufacturers build SCSI devices that
  self-terminate

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Protecting Data with RAID

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Protecting Data

• The most important part of a PC is the data it
  holds
• Companies have gone out of business because of
  losing data on hard drives
• Hard drives will eventually develop faults
• Fault tolerance allows systems to operate even
  when a component fails
• Redundant Array of Inexpensive Disks (RAID) is
  one such technology

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RAID Level 0

• Disk striping
• Writes data across multiple drives at once
• Requires at least two hard drives
• Provides increased read and writes
• Not fault tolerant
• If any drive fails, the data is lost

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RAID Level 1

• Disk mirroring/duplexing is the process of
  writing the same data to two drives at the same
  time
• Requires two drives
• Produces an exact mirror of the primary drive
• Mirroring uses the same controller
• Duplexing uses separate controllers

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RAID Levels 2 to 4

• RAID 2
• Disk striping with multiple parity drives
• Not used
• RAID 3 and 4
• Disk striping with dedicated parity
• Dedicated data drives and dedicated parity drives
• Quickly replaced by RAID 5

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RAID Level 5

• Disk striping with distributed parity
• Distributes data and parity evenly across the
  drives
• Requires at least three drives
• Most common RAID implementation

Software-based RAID 5
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RAID 5 (Stripe with Parity)
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RAID Level 6

• Super disk striping with distributed parity
• RAID 5 with asynchronous and cached data
  capability

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Implementing RAID

• SCSI has been the primary choice in the past
• Faster than PATA
• PATA allowed only four drives
• SATA today viewed as comparable choice
• Speeds comparable to SCSI
• Dedicated SATA controllers can support up to 15
  drives

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Hardware vs. Software

• Hardware RAID
• Dedicated controller
• Operating system views it as single volume
• Software RAID
• Operating system recognizes all individual
  disks
• Combines them together as single volume

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Personal RAID

• ATA RAID controller chips have gone down in price
• Some motherboards are now shipping with RAID
  built-in
• The future is RAID
• RAID has been around for 20 years but is now less
  expensive and moving into desktop systems

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THANK YOU