In-depth Look at Computer Storage Devices, Speed, and Disk Access Techniques - Prof. C. Hu, Study notes of Computer Science

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CSCE 210: Computer Hardware Foundations Chin-Tser Huang huangct@cse.sc.edu University of South Carolina Chapter 10: Computer a Peripherals 10/29/2009 5 Speed  Measured by access time and data transfer rate  Access time: average time it takes a computer to locate data and read it  millisecond = one-thousandth of a second  Data transfer rate: amount of data that moves per second Storage Hierarchy Increasing storage capacity 10/29/2009 Device Typical access times CPU registers 0.25 nsec Cache memory (SRAM) 1-10 nsec Conventional memory (DRAM) | 10-50 nsec Flash memory 120 jsec Magnetic disk drive 10-50 msec Optical disk drive 100-500 msec Magnetic tape 0.5 and up sec Increasing access times 10/29/2009 7 Secondary Storage Devices  Solid state memory  Magnetic disks  Optical disk storage  Magnetic tape  Network storage  Characteristics  Rotation vs. Linear  Direct access vs. Sequential access a" Hard Disk Layout Platter Sector Track ees Cylinder —= Head, on moving arm 10/29/2009 i 10 10/29/2009 11 Techniques for Accessing a Disk  CAV – Constant Angular Velocity  Number of bits on each track is the same! Denser towards the center  Spins the same speed for every track  CLV – Constant Linear Velocity  All tracks have the same physical length and number of bits  Constant speed reading data off a track  Drive has to speed up when accessing close to the center of the drive and slow down when accessing towards the edge of the drive 10/29/2009 12 A Newer Technique: Multiple Zone  Multiple zone recording  Also known as zone bit recording (ZBR) or zone- CAV recording (Z-CAV)  Compromise between CAV and CLV  Disk divided into zones  Cylinders in different zones have a different number of sectors  Number of sectors in a particular zone is constant  Data is buffered so the data rate to the I/O interface is constant 10/29/2009 15 Disk Access Times  Average Seek time  average time to move from one track to another  Average Latency time  average time to rotate to the beginning of the sector  Average Latency time = ½ * 1/rotational speed  Transfer time  1/(# of sectors * rotational speed)  Total Time to access a disk block  Avg. seek time + avg. latency time + avg. transfer time 10/29/2009 16 Disk Data Format  Data Block Format  Interblock gap  Header  Data – 512 bytes  Formatting disk  Establishes the track positions, blocks and headers needed before use of the disk 10/29/2009 17 Disk Block Formats Single Data Block Header for Windows disk 10/29/2009 20 RAID – Striped  A file segment is stored divided into blocks on different disks  Minimum of three drives needed because one disk drive is reserved for error checking  Writes – block of parity words from each block of data is created and put on the reserved error checking disk  Reads – parity data is used to check original data 10/29/2009 21 RAID Levels  RAID 0 – not true RAID, no error checking or redundancy, but data is placed across all drives for increased speed  RAID 1 – mirrored array  RAID 2, 3, 4 – arrays that are striped in different ways  RAID 5 – error checking blocks are spread across all drives 10/29/2009 22 Optical Storage  Reflected light off a mirrored or pitted surface  CD-ROM  650 MB of data, approximately 550 MB after formatting and error checking  Spiral 3 miles long, containing 15 billion bits!  CLV – all blocks are same physical length  Block – 2352 bytes  2K of data (2048 bytes)  16 bytes for header (12 start, 4 id)  288 bytes for advanced error control  DVD – similar technology to CD-ROM, but data packing is tighter 10/29/2009 25 Layout: CD-ROM vs. Standard Disk CD-ROM Hard Disk 10/29/2009 26 Types of Optical Storage  WORM Disks  Write-once-read-many times  Medium can be altered by using a medium-powered laser to blister the surface  Medium-powered laser blister technology also used for  CD-R, DVD-R, DVD-R, DVD+R  CD-RW, DVD-RW, DVD+RW, DVD-RAM, DVD+RAMBD- RE  File compatibility issues between the different CD, DVD and WORM formats 10/29/2009 27 Magnetic Tape  Offline storage  Backup and archival purposes  Disaster recovery  Tape Cartridges  Linear tape open format vs. helical scan tape format Color Transformation ae he 123 Value of pixel to be displayed { { | 65to Oto 177 to red green blue display display display Renn Pixel value R G B Blue-violet displayed 10/29/2009 30 Interlaced vs. Progressive Scan Interlaced scan Progressive scan Horizontal Vertical retrace retrace 10/29/2009 31 Diagram of Raster Screen Generation Process CPU program loads memory with image to line O line 1 Palette table WO) @) 0 Video display line M-1 a - — Time be displayed pixel (0,0) pixel (0,1) pixel (0, N-1) Memory Video scanner memory Consecutive pixel (M-1,0) addresses are produced | pixel (M-1, N-1) repetitively Scan generator 10/29/2009 Liquid Crystal Display rquid Color Polarizing cry: filters filter Glass cells plate Polarizing Fluorescent filter light panel 10/29/2009 35 10/29/2009 36 LCDs (continued)  Active matrix  One transistor per cell  More expensive  Brighter picture  Passive matrix  One transistor per row or column  Each cell is lit in succession  Display is dimmer since pixels are lit less frequently 10/29/2009 37 CRT Display Technology  CRTs (similar to TVs)  3 stripes of phosphors for each color  3 separate electron guns for each color  Strength of beam  brightness of color  Raster scan  30x per second  Interlaced vs. non-interlaced (progressive scan) 4 Creating a Gray Scale ns es es ns black 10/29/2009 40 10/29/2009 41 Laser Printer Operation 1. Dots of laser light are beamed onto a drum 2. Drum becomes electrically charged 3. Drum passes through toner which then sticks to the electrically charged places 4. Electrically charged paper is fed toward the drum 5. Toner is transferred from the drum to the paper 6. The fusing system heats and melts the toner onto the paper 7. A corona wire resets the electrical charge on the drum Laser Printer Operation (7 Ong spinning photosensitive mirror drum O 10/29/2009 1. A laser is firad in correspondence to the dots that are to be printed. A spinning mirror causes the dots to be fanned cut across the drum. The drum rotates to create the next line, usually 1/S00th or 1/6001 of an inca. The drum is photosensitive. As a result of the lager light, the drurn will hecame electrically charged wherever a dot is to be printec, . As the drum continues to rotate, the charged part of the drum passes through a tank of black powder called toner, Toner sticks to the drum wherever the charge is present. Thus, it looks like the image. 42