Computers12 Ch6


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Computers12 Ch6

  1. 1. Chapter 6 B.M.H Storage and Multimedia
  2. 2. Index <ul><li>Secondary Storage </li></ul><ul><li>Magnetic Disk Storage </li></ul><ul><ul><li>Diskettes </li></ul></ul><ul><ul><li>Hard Disks </li></ul></ul><ul><li>Data Organization on a Disk </li></ul>
  3. 3. Computer System <ul><li>Hardware </li></ul><ul><ul><li>Input devices </li></ul></ul><ul><ul><li>Output devices </li></ul></ul><ul><ul><li>Processor and Memory </li></ul></ul><ul><ul><li>Secondary Storages </li></ul></ul><ul><li>Software </li></ul><ul><ul><li>System SW </li></ul></ul><ul><ul><li>Applications SW </li></ul></ul><ul><li>People </li></ul>
  4. 4. Computer system Input Processing Output Secondary Storage
  5. 5. Secondary Storage <ul><li>Benefits </li></ul><ul><ul><li>Space </li></ul></ul><ul><ul><li>Reliability </li></ul></ul><ul><ul><li>Convenience </li></ul></ul><ul><ul><li>Economy </li></ul></ul>
  6. 6. Secondary Storage <ul><li>Types </li></ul><ul><ul><li>Magnetic disk storage </li></ul></ul><ul><ul><ul><li>Diskettes, Hard Disks </li></ul></ul></ul><ul><ul><li>Magnetic tape storage </li></ul></ul><ul><ul><li>Optical disk storage </li></ul></ul><ul><ul><ul><li>CD, DVD </li></ul></ul></ul>
  7. 7. Magnetic Disk Storage <ul><li>Magnetic media </li></ul><ul><ul><li>a technology of representing data as magnetized spots on the surface of a spinning disk </li></ul></ul><ul><ul><ul><li>A magnetized spot : 1 bit </li></ul></ul></ul><ul><ul><ul><li>The absence of such a spot : 0 bit </li></ul></ul></ul>
  8. 8. Magnetic Disk Storage <ul><li>Reading data from the disk </li></ul><ul><ul><li>Converting the magnetized data to electrical impulses </li></ul></ul><ul><li>Writing data to disk </li></ul><ul><ul><li>Converting electrical impulses from the processor to magnetized spots on the disk </li></ul></ul>
  9. 10. Magnetic Disk Storage <ul><li>Types </li></ul><ul><ul><li>Diskettes </li></ul></ul><ul><ul><li>Hard disks </li></ul></ul>
  10. 11. Diskettes <ul><li>Made of flexible Mylar </li></ul><ul><li>Coated with iron oxide, </li></ul><ul><ul><li>a substance that can be magnetized </li></ul></ul><ul><li>Types </li></ul><ul><ul><li>The standard floppy disk : </li></ul></ul><ul><ul><ul><li>3 1/2-inch diskette 1.44 megabytes of data </li></ul></ul></ul><ul><ul><li>Two new high-capacity drives : </li></ul></ul><ul><ul><ul><li>120 or 200 megabytes per disk </li></ul></ul></ul><ul><ul><li>Iomega’s Zip drive : </li></ul></ul><ul><ul><ul><li>250-megabyte disks </li></ul></ul></ul><ul><ul><ul><li>Is not compatible with 31/2-inch diskettes </li></ul></ul></ul>
  11. 16. Hard Disk <ul><li>A rigid platter coated with magnetic oxide </li></ul><ul><li>Sizes : various </li></ul><ul><li>Capacity for PC </li></ul><ul><ul><li>Older ones : hundreds of megabytes </li></ul></ul><ul><ul><li>New ones : tens of gigabytes of storage </li></ul></ul>
  12. 17. Hard Disk <ul><li>Disk pack </li></ul><ul><ul><li>assembles several platters </li></ul></ul><ul><ul><li>Components </li></ul></ul><ul><ul><ul><li>Platters </li></ul></ul></ul><ul><ul><ul><li>Access arms </li></ul></ul></ul><ul><ul><ul><li>Read/write heads </li></ul></ul></ul>
  13. 21. Hard Disks in Groups <ul><li>RAID </li></ul><ul><ul><li>( R edundant A rray of I ndependent d isks) </li></ul></ul><ul><ul><li>Uses a group of small hard disks that work together as a unit </li></ul></ul><ul><ul><li>Used for storage system to be safe </li></ul></ul><ul><ul><li>Types </li></ul></ul><ul><ul><ul><li>RAID level 1 </li></ul></ul></ul><ul><ul><ul><li>Higher levels of RAID </li></ul></ul></ul>
  14. 22. Data organization on a disk <ul><li>Several characteristics </li></ul><ul><ul><li>Track </li></ul></ul><ul><ul><li>Sectors </li></ul></ul><ul><ul><li>Clusters </li></ul></ul><ul><ul><li>Cylinder </li></ul></ul>
  15. 29. Disk drive <ul><li>A device that allows data to be read from a disk or written to a disk </li></ul><ul><li>The performance </li></ul><ul><ul><li>One measure : average access time </li></ul></ul><ul><ul><li>Another measure : data transfer rate </li></ul></ul>
  16. 31. Access Time <ul><li>The time needed to access data directly on disk </li></ul><ul><li>Three primary factors </li></ul><ul><ul><li>Seek time </li></ul></ul><ul><ul><li>Head switching </li></ul></ul><ul><ul><li>Rotational delay </li></ul></ul><ul><li>Average access time </li></ul><ul><ul><li>Usually measured in milliseconds (ms) </li></ul></ul><ul><ul><li>Current hard disk drives : Under 10ms </li></ul></ul>
  17. 32. Data transfer <ul><li>The process of transferring data between memory and the place on the disk track </li></ul><ul><ul><li>Writing : from memory to the track </li></ul></ul><ul><ul><li>Reading : from the track to memory </li></ul></ul><ul><li>Data transfer rate </li></ul><ul><ul><li>Tells how fast data can be transferred once it has been found </li></ul></ul><ul><ul><li>Usually be measured in megabytes of data per second </li></ul></ul>
  18. 33. Disk Cache <ul><li>Used to improve the effective access time </li></ul><ul><li>Memory cache </li></ul>