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Computer SCIENCE

Data Representation and Machine Concepts. Computer SCIENCE. Section 1.3. Instructor: Lin Chen. August 2013. 1 Data Storage. 1.3 Mass Storage. Magnetic Systems Optical Systems Flash Drives File Storage and Retrieval.

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Computer SCIENCE

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  1. Data Representation and Machine Concepts Computer SCIENCE Section 1.3 Instructor: Lin Chen August 2013

  2. 1 Data Storage 1.3 Mass Storage Magnetic Systems Optical Systems Flash Drives File Storage and Retrieval Pearson Custom: Computer Science, Data Representation and Machine Concepts

  3. 1.3 Mass Storage Introduction Mass Storage Additional memory, secondary storage Including magnetic disks, CDs, DVDs, magnetic tapes, and flash drives Advantages Less volatility Large storage capacityies Low cost The ability to be removed

  4. 1.3 Mass Storage Introduction Terms On-Line The device or information is connected and readily available to the machine without human intervention Off-Line Human intervention is required before the device or information can be accessed by the machine

  5. 1.3 Mass Storage Magnetic System Uses a thin spinning disk with magnetic coating to hold data Hard drive Floppy drive Tape Sequential changes in the direction of magnetization represent binary data0 and 1 http://en.wikipedia.org/wiki/Hard_disk_drive#Magnetic_recording

  6. 1.3 Mass Storage Magnetic System Hard Drive http://www.computer-hardware-explained.com/computer-hard-drive.html

  7. 1.3 Mass Storage Magnetic System Hard Drive Several platters are fixed on same spindle Track, each circle lane Sector, each track is divided into small arcs Read/Write head are placed above and below each disk Spindle http://users.dickinson.edu/~braught/courses/cs354s10/topics/slides/06-filesystems.pdf

  8. 1.3 Mass Storage Magnetic System Hard Drive Information on each sector is a continuous String of bits All sector contain the same number of bits (512 Bytes to a few KB) The tracks near the outer edge can contains more sectors due to the longer perimeter Spindle http://users.dickinson.edu/~braught/courses/cs354s10/topics/slides/06-filesystems.pdf

  9. 1.3 Mass Storage Magnetic System Hard Drive Formatting Procedure initializing the location of tracks and sectors Low-level formatting Establish the tracks and sectors on the disk, the starting end ending points of each sector are written onto the platter High-level formatting Write the file-storage structures, prepares the drive to hold files

  10. 1.3 Mass Storage Magnetic System Hard Drive Access time Seek time (~ 4ms) the time required to move the read/write heads from on track to another Rotational latency (~ 5ms) half the time required for the disk to make a complete rotation Transfer time (MB per second, fastest) the rate at which data can be transferred to or from the disk

  11. 1.3 Mass Storage Magnetic System Hard Drive Access time Seek time (~ 4ms) the time required to move the read/write heads from on track to another Rotational latency (~ 5ms) half the time required for the disk to make a complete rotation Transfer time (MB per second, fastest) the rate at which data can be transferred to or from the disk Why?

  12. 1.3 Mass Storage Magnetic System Hard Drive Calculate the hard drive size: A hard drive has 10 platters, each platter has 200 tracks, each tracks has same number of sectors, each sectors can save 512 bytes, what is the size of this hard drive?

  13. 1.3 Mass Storage Magnetic System Hard Drive Suppose that a disk drive has 5000 cylinders, numbered 0 to 4999. The drive is currently serving a request at cylinder 143, and the previous request was at cylinder 125. The queue of pending requests, in FIFO order, is 86, 1470, 913, 1774, 948, 1509, 1022, 1750, 130 Starting from the current head position, what is the total distance (in cylinders) that the disk arm moves to satisfy all the pending requests? http://web.cs.du.edu/~dconnors/courses/comp3361/assignments/ch12.pdf

  14. 1.3 Mass Storage Magnetic System Floppy Disk http://en.wikipedia.org/wiki/File:Floppy_disk_2009_G1.jpg

  15. 1.3 Mass Storage Magnetic System Floppy Disk Single plastic disk 3 1/2 floppy disk has capacity of 1.44 MB Off-line device Question: how many tracks in above floppy disk, suppose each sector contains 512 bytes

  16. 1.3 Mass Storage Magnetic System Magnetic Tape Access data by a tape drive, which can read, write, and rewind the tape Size can be several GB Disadvantage: Reading between two different positions on a tape is time-consuming Off-line device http://en.wikipedia.org/wiki/File:Ibm-729v.jpg

  17. 1.3 Mass Storage Optical Systems Compact Disk CD-DA (Compact Disk-Digital Audio) store and play back sound recording CD-ROM (CD Read-Only Memory) store data CD-R write-once audio CD-RW rewritable media VCD video compact disc DVD digital optical disc storage

  18. 1.3 Mass Storage Optical Systems Compact Disk http://www.clker.com/clipart-3223.html

  19. 1.3 Mass Storage Optical Systems Compact Disk 12 centimeters in diameter Single track that spirals around the CD The track is divided into sectors, each sector contains 2KB data http://electronics.howstuffworks.com/cd2.htm

  20. 1.3 Mass Storage Optical Systems Compact Disk A polycarbonate disc layer has the data encoded by using bumps A shiny layer reflects the laser A layer of lacquer protects the shiny Artwork is screen printed on the top of disc A laser bean reads the CD http://en.wikipedia.org/wiki/File:CD_layers.svg

  21. 1.3 Mass Storage Optical Systems Compact Disk Data is represented as tiny indentations known as “pits” DVD http://www.clir.org/pubs/reports/pub121/sec3.html http://en.wikipedia.org/wiki/File:Comparison_CD_DVD_HDDVD_BD.svg

  22. 1.3 Mass Storage Flash Drives Chambers of silicon dioxide capture the electrons to represent the binary number Hold data for many years Too many erasing could damages the silicon dioxide chamber Not sensitive to physical shock (portable) http://data-recovery-weekly.blogspot.com/2010/06/fake-flash-drive.html http://tohii.blog.china.com/201203/9424017.html

  23. 1.3 Mass Storage File Storage and Retrieval Physical Record A block of data conforming to the specific characteristics of a determined size Logical Record Naturally occurring blocks of data

  24. 1.3 Mass Storage File Storage and Retrieval File1 File2 Physical Record On Hard Disk File1 File2 Observed in system Logical Record

  25. 1.3 Mass Storage File Storage and Retrieval Piece 1 Piece 2 Physical Record On Hard Disk Observed in system Logical Record File

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