Day 4: Data Storage (ppt)
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Day 4: Data Storage (ppt)

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Day 4: Data Storage (ppt) Day 4: Data Storage (ppt) Presentation Transcript

  • Data Storage CSci 131 Sept. 12, 2006
  • Outline
    • Bytes
    • Main Memory
    • Mass Storage
    • Comparison
    • Quiz1 – 10 min
  • Bit Review
    • Flip-flops and capacitors provide means for storing a bit
    • Flash memory – electrons are trapped inside tiny chambers
      • Two states are full or empty chambers
    • Flip flops, cores, capacitors are forms of dynamic memory
    • Flash memory holds the data “permanently”
  • Bytes
    • Byte is 8 ordered bits
      • 10000000 and 00000001 are different
    • The left end is the high-order end and the leftmost bit is the most significant bit
    • The right end is the low-order end and the rightmost bit is the least significant bit
  • Storage Measurements
  • Example
    • A file is 5,376,000 bytes long
      • How many kilobytes (KB) is this?
      • How many megabytes (MB) is this?
  • Main Memory
    • Main memory is a sequence of cells that can hold 1 byte
    • Each cell has a unique numerical address
    • Main memory is ordered
  • Main memory
    • Consecutive bytes (cells) are used for larger data
  • Properties of main memory
    • Random Access Memory – RAM
      • each cell or memory location can be referenced, accessed, or modified in the same amount of time
    • Memory is very fast
      • Access time is measured in nanoseconds
    • Memory is volatile
      • Contents disappear when power is gone
  • Mass Storage
    • Also called Secondary Memory
    • Much larger and cheaper than RAM
    • Data contents remain after power is disconnected
    • Access times are slower (in milliseconds) since secondary storage relies on mechanical motion
  • Types of Mass Storage
    • Hard disk
    • Floppy disk
    • Zip Disk
    • CD
    • DVD
    • Flash drive
  • Disk Storage
    • Each surface of a disk has magnetic coating
    • The surface is divided into rings called tracks
    • Each track is broken down into sectors
      • Every track on a disk has the same number of sectors
      • Each sector holds the same amount of data
  • Disk Storage
  • Disk Storage
    • Disk spins while a read/write head moves in and out to view different areas
    • Types:
      • Hard disks: not removable, fast, primary storage
      • Floppy/Zip disks: removable, slower, used for distribution or backup
  • Disk Access
    • Move read/write head to proper track
    • Wait for disk to spin and sector to move under read/write head
    • Read from (write to) the sector as it passes under the read/write head
  • Disk Access Terms
    • Seek time : time to move read/write head between tracks
    • Latency time : time for ½ disk rotation
    • Access time : seek time + latency time
    • Transfer rate : rate at which data can be transferred to/from disk
  • Compact Disc (CD)
    • Uses optical technology instead of magnetic discs
    • Each CD is a spinning, 5 in. diameter disc with reflective material and protective coating
    • Writing requires a laser creating variations on the surface
    • Reading uses a laser and mirrors to monitor the surface of the CD
  • Compact Disc (CD)
    • CD is a single track that spirals where a hard drive was multi-track
    • All sectors are the same size
      • Benefit of better storage space use
      • Drawback of slower access time
    • Main types: CD-ROM, CD-R, CD-RW, DVD
  • Tape Storage
    • Long plastic band with magnetic coating
    • Organized into blocks separated by inter-record gaps
      • Blocks store data
      • Inter-record gaps help seeking
  • Tape Storage
    • Tape access is linear .
    • Tape must be wound until needed block is under the read/write head.
    • Tapes are slow but can hold large amounts of data
    • Used primarily as backups for hard drives
  • Comparison
  • Assignment for 09/14
    • Read Sections 1.4, 1.5
    • HW1 due Thurs. 14 (next class)
    • Quiz1 now
  • Main Memory
    • Want as much fast storage as possible
    • But RAM is volatile
    • Disk slower but larger and non-volatile
    • Cost
    • Engineering
    • Why 1GB of RAM? 100 GB hard-drive?