ITE 272 Introduction to Information Technology Part II

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ITE 272 Introduction to Information Technology
Part II

• Chapter 5
• Data Storage Technology

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Storage Device Characteristics

• Speed
• Volatility
• Access method
• Portability
• Cost and capacity

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Storage Device Characteristics
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Storage Device Characteristics

• Speed
• Primary Storage
• Wait state
• Secondary Storage
• Access time
• Data transfer rate

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Storage Device Characteristics

• Volatility
• A storage device or medium is non-volatile if it
  holds data without loss over long periods of
  time.
• A storage device or medium is volatile if it
  cannot reliably hold data for long periods of
  time.

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Storage Device Characteristics

• Access Methods
• Serial Access
• Stores and retrieves data items in a linear
  order. (Magnetic tape)
• Random Access
• Access device is not restricted to any specific
  order when accessing data. (Hard Disk)
• Parallel Access
• Device that is capable of simultaneously
  accessing multiple storage locations. (Random
  Access Memory)

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Storage Device Characteristics
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Storage Device Characteristics
Memory Storage Hierarchy
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Primary Storage Devices

• Storing Electrical Signals
• Random Access Memory
• Read-Only Memory
• Memory Packaging

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Primary Storage Devices

• Storing Electrical Signals
• Data is represented as electrical signals.
• Digital signals are used to transmit data to and
  from devices attached to the system bus.
• Storage devices must accept electrical signals as
  input and output.

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Primary Storage Devices

• Random Access Memory Characteristics
• Microchip implementation using semiconductors
• Ability to read and write with equal speed
• Random access to stored bytes, words, or larger
  data units

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Primary Storage Devices

• Types of RAM
• Static RAM (SRAM)
• Dynamic RAM (DRAM)
• Synchronous DRAM (SDRAM)
• Enhanced DRAM (EDRAM)

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Primary Storage Devices
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Primary Storage Devices

• Read-Only Memory
• Device that can store data permanently or semi
  permanently.
• Firmware
• EEPROM
• Flash

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Primary Storage Devices
Memory Packaging
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CPU Memory Access

• Physical Memory Organization
• Main memory can be regarded as a sequence of
  contiguous, or adjacent memory cells.
• Addressable memory vs. physical memory

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CPU Memory Access
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CPU Memory Access

• Memory Allocation and Addressing
• Describes the assignment of specific memory
  addresses to system software, application
  programs and data.

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CPU Memory Access
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CPU Memory Access

• Memory Addressing
• Absolute Addressing
• describes memory address operands that refer to
  actual physical memory locations.
• Relative Addressing (Indirect Addressing)
• automatically computes physical memory addresses.
  

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CPU Memory Access
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Secondary Storage Magnetic

• Magnetic Storage
• Exploit the duality of magnetism and electricity.
• Electric current is used to generate a magnetic
  field.
• A magnetic field can be used to generate
  electricity.

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Secondary Storage Magnetic
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Secondary Storage Magnetic
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Magnetic Storage
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Secondary Storage Magnetic

• Magnetic Tape
• Ribbon of plastic with a coercible surface
  coating.
• Mounted in a tape drive for reading and writing.
• Compound the magnetic leakage problem by winding
  the tape upon itself.
• Another issue - stretching

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Magnetic Storage
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Magnetic Storage
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Secondary Storage Magnetic

• Magnetic Disk
• Flat circular platters with metallic coatings
  that are rotated beneath read/write heads
• Multiple platters can be mounted
• Once concentric circle is a track
• A fractional portion of a track is a sector
• A cylinder is the set of all tracks at an
  equivalent distance from the edge or spindle on
  all platter surfaces

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Secondary Storage Magnetic

• Magnetic Disk Types
• Hard Disk
• magnetic disk media with a rigid metal base.
• Floppy Disk (Diskette)
• uses a base of flexible or rigid plastic
  material.

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Secondary Storage Magnetic
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Secondary Storage Magnetic
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Secondary Storage Magnetic
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Secondary Storage Magnetic

• Access Time
• Elapsed time between the receipt and completion
  of a read or write command
• Head-to-Head Switching Time
• Elapsed time required to switch shared read/write
  circuitry between two adjacent read/write heads
• Track-to-Track Seek Time
• Time required to move a disk read/write head
  between two adjacent tracks

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Secondary Storage Magnetic

• Rotational Delay
• Waiting time for the desired sector of a disk to
  rotate beneath a read/write head
• Sequential Access Time
• Time required to access the second of a stored
  sequential pair of data items
• Sustained Data Transfer Rate
• Maximum data transfer rate that can be sustained
  by a device or a communications channel during
  lengthy data transfer operations

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Secondary Storage Magnetic

• Maximum Data Transfer Rate
• The maximum speed storage device can move data to
  device (Assumes sequential access)
• Average Access Time
• Statistical average elapsed time required by a
  storage device to respond to a read or write
  command

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Secondary Storage Magnetic

• Average Access Delay
• HTH Switch TTT Seek Rotation Delay
• Average Access Time
• Average Access Delay Time required to read a
  single sector
• Data Transfer Rate
• 1/Access Delay Data Transfer Units (Max)
• 1/Access Time Data Transfer Unit (Sustained)

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Secondary Storage Optical

• Advantages
• Higher recording density
• Longer data life
• Retain data for decades
• Not subject to problems of magnetic decay and
  leakage

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Secondary Storage Optical

• Optical storage devices store bit values as
  variations in light reflection.
• Storage medium is a surface of highly reflective
  material.
• The read mechanism consists of a low-power laser
  and a photoelectric cell.

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Secondary Storage Optical
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Secondary Storage Optical
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The End