Day 4: Data Storage (ppt)


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Day 4: Data Storage (ppt)

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