EET 450 - Advanced Digital

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EET 450 - Advanced Digital

• Chapter 8
• Mass Storage

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Technologies

• One of the primary blocks of the computer
  system is Mass Storage.
• Store large amounts of Data and Program
  information, available quickly
• Not as fast as Main Memory
• Speeds can be improved with Cache

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Technologies

• Magnetic
• can detect the change of a magnetic field
• motion
• varying field
• A wire must break the lines of magnetic flux
• Materials
• iron, nickel, cobalt

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Technologies

• materials dictate issues of speed (coercivity),
  life of stored information (retentivity)
• Magneto-Optical
• use laser to direct magnetic field in recording
  data image
• laser alone is used to read
• Very high storage density

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Technologies

• Optical
• CD technology used to optically record and read
  digital information.
• CD
• DVD
• CDR
• CDRW

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Types of Mass Storage

• Hard Disks
• Floppy Disks
• PC Cards
• Magneto-optical Drives
• CD-Rom/CDR/CDRW
• DVD ROM / DVD Ram
• Tape Drives

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• Magnetic
• Optical
• Solid State

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Access

• Random Access
• Any bit w/in access time for device
• Sequential
• Tape drive
• New Technologies
• DVD - optimized for sequential access, but does
  random

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Magnetic Media

• Based on some form of magnetic compound
• Wire
• Tape - mylar with magnetic compound adhered to
  it.
• Disks/Drums/Platters

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Magnetic Media

• magnetism and electricity are related
• moving a wire in a magnetic field generates
  electrical current
• running a current through an electrical wire
  produces a magnetic field
• The magnetic materials - iron, nickel, cobalt are
  the common ones - consist of small particles with
  magnetic properties

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Magnetic Media

• At the small level, these particles can be viewed
  as a group of little magnets.
• These little magnets are originally in Random
  order.
• By imposing a magnetic field, the little magnets
  line up.
• When these lined up magnets are MOVED near a wire
  electricity.

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Magnetic Media
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Magnetic Media

• The affect of magnetic field or induced current
  is magnified at a gap
• Only a change in magnetic field can be detected
• These CHANGES are used to encode digital
  information

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Recording Methods

• to record magnetic information, a timed sequence
  of flux transitions occurs.
• Recording
• Frequency Modulation - FM
• Modified Frequency Modulation - MFM
• Saves space by eliminating clock pulses
• Run Length Limited - RLL

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Drives

• Older technology drives were delivered
  unformatted
• Using a low level program, the drive was
  formatted - writing sector information and tracks
• The disk would then be partitioned
• The OS must then format the partition
• Current versions - IDE, Ultra, SCSI, etc. do not
  require low level formatting.

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Drives

• Various methods of data compression have been
  used to increase storage space
• compression, typically software based, took up
  speed by loading the main processor with
  compression/decompression responsibilities.

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Hard Drives

• Increased storage has been gained, by advanced
  formulations of magnetic compounds.
• more precise movement in mechanisms
• more precise manufacturing - leading to smoother,
  more even emulsion layers.
• Fast rotation speeds and powerful head movement
  mechanisms

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Advanced Storage Systems

• Drive Arrays
• RAID
• Parallel Access Arrays
• Magneto-Optical systems
• Optically assisted magnetic write with, optical
  read
• magnetically erased
• SLOW

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Drive Interfaces

• The physical drive has limitations for size and
  speed.
• The electronic connection to the system imposes
  its own limitations.
• See Table 9.1
• note that transfer rate is the only figure of
  merit in this table (besides of devices)

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Table 9.1
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Drive interfaces

• Note P1394 - fire wire
• FC-AL Fiber Channel-Arbitrated Loop
• SSA System Storage Arch.
• Aaron -a blend of fiber connections
• Current USB is being used
• see Apple G3

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Performance of AT drives

• see Table 9.2
• speeds to 16 Mbps

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Table 9.2
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Addressing Limit

• Legacy limit of drive size -
• DOS imposed
• 504Mb limit
• Solution - bypass INT13h access of drives

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ATAPI

• AT Attachment interface with Packet control
  commands
• for CDRom and Tape drives

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Implementations

• ATA
• EIDE
• ATA-2 (Fast-ATA)
• Up to 137.4 GB
• ATA-3
• Added S.M.A.R.T. (Self-Monitoring, Analysis and
  Reporting Technology)

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ATA/ATAPI

• ATA/ATAPI-4 Packet Int. Ext
• Defined 80 cond. 40 pin cable
• UDMA/33
• Enhanced BIOS for over 9.4 trillion gigabytes
  (ATA is still lt 137.4GB)
• ATA/ATAPI-5 w/ Packet Int.
• Requires 80 conductor cable for UDMA/66

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Physical Wiring

• Drive Cables
• Terminated cable end
• 40 pin cable - ribbon
• 44 pin connector - pins 41-44 provide power
• 50 pin variant - provides drive selection
• 68 pin connector - PC Card
• Pin assignments - see table 9.7
• Power

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Master/Slave selection

• ATA - supports two drives per channel
• Choices
• Master
• Slave
• Only Drive

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SCSI

• Small Computer System Interface
• SCSI-1,2,3
• Advanced SCSI
• Wide SCSI - 32 bit wide
• Ultra SCSI 10 MHz timing - 40 Mb/sec transfer
• Table 9.11 - transfer rate versus Cable length
• Addressing 15 devices

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Table 9.11
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SCSI

• Termination
• See figure 9.12 - page 459
• Connectors
• 25 pin D type connectors
• 50 pin amphenol
• 68 pin - Wide SCSI-2/3 devices

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Floppy Drive connections

• 34 pin ribbon
• termination
• twist

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Power Connections

• 12 V for motor controls on some drives
• 5 V for logic
• Some older drives with ROM on board may require
  -12v, etc. but this is not typical in todays
  systems.
• Two connector types - D shaped, 3.5 inch drive
  type

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Other connections

• legacy connections - MFM/RLL type
• separate data cables