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EET 450 - Advanced Digital. Chapter 8 Mass Storage. 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. Technologies. Magnetic

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EET 450 - Advanced Digital

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EET 450 - Advanced Digital

Chapter 8

Mass Storage


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


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


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


  • Technologies

    • Optical

      • CD technology used to optically record and read digital information.

        • CD

        • DVD

        • CDR

        • CDRW


    Types of Mass Storage

    • Hard Disks

    • Floppy Disks

    • PC Cards

    • Magneto-optical Drives

    • CD-Rom/CDR/CDRW

      • DVD ROM / DVD Ram

    • Tape Drives


    • Magnetic

    • Optical

    • Solid State


    Access

    • Random Access

      • Any bit w/in access time for device

    • Sequential

      • Tape drive

    • New Technologies

      • DVD - optimized for sequential access, but does random


    Magnetic Media

    • Based on some form of magnetic compound

      • Wire

      • Tape - mylar with magnetic compound adhered to it.

      • Disks/Drums/Platters


    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


    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.


    Magnetic Media


    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


    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


    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.


    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.


    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


    Advanced Storage Systems

    • Drive Arrays

      • RAID

    • Parallel Access Arrays

    • Magneto-Optical systems

      • Optically assisted magnetic write with, optical read

      • magnetically erased

      • SLOW


    Drive Interfaces

    • The physical drive has limitations for size and speed.

    • The electronic connection to the ‘system’ imposes it’s own limitations.

    • See Table 9.1

      • note that transfer rate is the only figure of merit in this table (besides # of devices)


    Table 9.1


    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


    Performance of AT drives

    • see Table 9.2

      • speeds to 16 Mbps


    Table 9.2


    Addressing Limit

    • Legacy limit of drive size -

      • DOS imposed

    • 504Mb limit

    • Solution - bypass INT13h access of drives


    ATAPI

    • AT Attachment interface with Packet control commands

    • for CDRom and Tape drives


    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)


    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 <= 137.4GB)

    • ATA/ATAPI-5 – w/ Packet Int.

      • Requires 80 conductor cable for UDMA/66


    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


    Master/Slave selection

    • ATA - supports two drives per channel

    • Choices

      • Master

      • Slave

      • Only Drive


    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


    Table 9.11


    SCSI

    • Termination

      • See figure 9.12 - page 459

    • Connectors

      • 25 pin D type connectors

      • 50 pin amphenol

      • 68 pin - Wide SCSI-2/3 devices


    Floppy Drive connections

    • 34 pin ribbon

    • termination

    • twist


    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 today’s systems.

    • Two connector types - D shaped, ‘3.5 inch drive’ type


    Other connections

    • legacy connections - MFM/RLL type

      • separate data cables


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