Device Management - Chapter 7
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Questions and Answers

What is the purpose of the interrecord gap (IRG) in sequential access storage media?

  • To increase the data density on the tape
  • To provide a pause for the tape to stop between records (correct)
  • To enhance the transport speed of the tape
  • To allow error correction during data transfer

    • How does the blocking of records on magnetic tape impact its efficiency?

  • It increases the interblock gap (IBG)
  • It decreases the transport speed of the tape
  • It allows for simultaneous reading of all records
  • It reduces the total amount of tape required for storage (correct)

    • What contributes to the transfer rate of data on magnetic tape?

  • The tape density and transport speed (correct)
  • The size of the interrecord gaps
  • The number of characters recorded
  • The type of magnetic tape used

    • What is the effect of using an optimal block size on magnetic tape storage?

    <p>It allows entire blocks to fit in the buffer</p> Signup and view all the answers

    If each record requires 1 inch of tape, how much total tape is used when storing 10 records individually, accounting for IRGs?

    <p>5.5 inches</p> Signup and view all the answers

    What is the typical gap size inserted between each block in magnetic tape storage?

    <p>½ inch</p> Signup and view all the answers

    What is the maximum number of characters typically represented in a single inch of magnetic tape?

    <p>Thousands of characters</p> Signup and view all the answers

    When storing two blocks of records, what total length of tape is used if each block has an IBG of ½ inch and contains 10 records?

    <p>2.5 inches</p> Signup and view all the answers

    What is a key characteristic of CD-R technology?

    <p>Data is permanently written using a write-once technique.</p> Signup and view all the answers

    Which layer is NOT typically found in a DVD's structure?

    <p>Anodized layer</p> Signup and view all the answers

    How is data erased from a CD-RW disk?

    <p>By applying a low-energy beam to return the alloy to its crystalline state.</p> Signup and view all the answers

    What technology does CD-RW use for writing and erasing data?

    <p>Phase change technology.</p> Signup and view all the answers

    What is the primary function of the high-power laser in DVD technology?

    <p>To permanently mark the dye layer.</p> Signup and view all the answers

    What distinguishes CD-R from CD-RW technology?

    <p>CD-R is write-once, while CD-RW allows data to be erased and rewritten.</p> Signup and view all the answers

    Which statement about data reading on CD-DVD technologies is accurate?

    <p>A standard CD drive uses a low-power beam for reading data.</p> Signup and view all the answers

    What occurs when the beam heats the disc in CD-RW technology during data recording?

    <p>The disc's state changes from crystalline to amorphous.</p> Signup and view all the answers

    What is the role of the read/write heads in a magnetic disk system?

    <p>They are moved in unison by the arm to read or write data.</p> Signup and view all the answers

    Which of the following correctly describes the structure of a magnetic disk?

    <p>Each surface is divided into concentric tracks numbered from the center outwards.</p> Signup and view all the answers

    What must a system identify to access a specific record on a magnetic disk?

    <p>Cylinder number, surface number, and sector number.</p> Signup and view all the answers

    What is meant by 'virtual cylinder' in the context of magnetic disks?

    <p>A theoretical model for organizing tracks and sectors.</p> Signup and view all the answers

    How are the recording surfaces of a magnetic disk formatted?

    <p>Each surface is formatted prior to the recording of data.</p> Signup and view all the answers

    What is the best strategy for handling light loads?

    <p>F C F S</p> Signup and view all the answers

    Which strategy is identified as best for moderate loads?

    <p>S S T F</p> Signup and view all the answers

    What problem does the SCAN strategy eliminate?

    <p>Indefinite postponement</p> Signup and view all the answers

    Which strategy has very small service time variances under heavy loads?

    <p>C-SCAN</p> Signup and view all the answers

    Which feature does optical disc storage NOT have?

    <p>Variable sector sizes</p> Signup and view all the answers

    What is the key characteristic of the sectors on an optical disc?

    <p>They are of the same size throughout the disc.</p> Signup and view all the answers

    What is a limitation of the F C F S strategy under high loads?

    <p>Service time becomes unacceptably long.</p> Signup and view all the answers

    In terms of design, what does an optical disc drive do to maintain performance?

    <p>Changes speed to compensate for data density.</p> Signup and view all the answers

    What unit is used to measure the sustained data-transfer rate in optical disc storage?

    <p>Megabytes per second (Mbps)</p> Signup and view all the answers

    Which of the following best describes average access time in non-sequential data retrieval?

    <p>Time to move the read/write head to a specific disc location</p> Signup and view all the answers

    What is the significance of cache size in optical disc storage systems?

    <p>It affects the speed of data retrieval from the disc</p> Signup and view all the answers

    Which characteristic of data recorded on a CD describes the binary representation?

    <p>Pits and lands</p> Signup and view all the answers

    How does a photodetector function when reading data from a CD?

    <p>It converts light intensity into a digital signal</p> Signup and view all the answers

    What is the primary application requiring a sustained data-transfer rate?

    <p>Applications requiring sequential access</p> Signup and view all the answers

    What is indicated by the average access time measured in milliseconds (ms)?

    <p>Time to access a specific location on the disc</p> Signup and view all the answers

    In optical disc technology, what happens when light strikes a pit?

    <p>Light is scattered and absorbed</p> Signup and view all the answers

    What is the data capacity of a single-layer, single-sided DVD?

    <p>8.6 GB</p> Signup and view all the answers

    What distinguishes a Blu-ray Disc from DVD and CD in terms of laser technology?

    <p>Uses blue-violet laser</p> Signup and view all the answers

    Which format allows for rewritable data on a Blu-ray Disc?

    <p>BD-RE</p> Signup and view all the answers

    Which of the following statements is true regarding the physical design of DVDs in comparison to CDs?

    <p>DVDs and CDs have the same shape and size</p> Signup and view all the answers

    What does a dual-layer, single-sided DVD hold in terms of CD capacity?

    <p>13 CDs</p> Signup and view all the answers

    What technology is implemented in solid state storage to store electrons?

    <p>Fowler-Nordheim tunneling phenomenon</p> Signup and view all the answers

    What feature allows multiple layers to be used in Blu-ray technology?

    <p>Use of blue-violet laser</p> Signup and view all the answers

    What happens to the stored electrons in a solid state storage device when the power is turned off?

    <p>They remain even after power is turned off</p> Signup and view all the answers

    Study Notes

    Device Management - Chapter 7

    • The chapter covers different types of devices, including dedicated, shared, and virtual devices, and how they compare.
    • It also explains how blocking and buffering improve input/output (I/O) performance.
    • Seek time, search time, and transfer time calculation methods are described for various device types.
    • Discusses how different device access times vary and highlights the strengths and weaknesses of various seek strategies.
    • Explores different RAID levels and how they vary from each other.

    Types of Devices

    • Dedicated Device:
      • Assigned to one job at a time (e.g., tape drives, printers, plotters).
      • Inefficient if not used constantly.
    • Shared Device:
      • Assigned to multiple processes concurrently, as in the process of printing from multiple systems.
      • Processes share the device simultaneously.
      • Requests are interleaved by the device manager.
    • Virtual Device:
      • Combination of dedicated and shared devices.
      • Can be converted to sharable devices using spooling techniques.
      • Example includes converting a dedicated printer into a shared one using a queuing system.

    Sequential Access Storage Media

    • Magnetic Tape:
      • Routine secondary storage in early computer systems.
      • Records are stored serially, with a determined length by the application program.
      • Record access is time-consuming as tape rotates until the head reaches the desired record for reading/writing.
    • Sequential access storage media properties
      • Record access based on position on tape
      • Tape rotates passing under read/write head
      • Record length determined by application
      • Record identified by position on tape.
      • Time-consuming process.
      • Example of device: tapes

    Sequential Access Storage Media - Continued

    • Tape Density:
      • Characters or bytes recorded per inch of tape; impacted by storage method (individual or blocked records).
    • Interrecord Gap (IRG):
      • Gap inserted between records, necessary for the tape to stop before receiving the next record.
      • Size is consistent regardless of record size.
    • Interblock Gap (IBG):
      • Inserted between blocks of records; more efficient than having an IRG between individual records.

    Blocking Advantages and Disadvantages

    • Advantages:
      • Reduced I/O operations-one READ instruction moves an entire block
      • Less space used on tape
    • Disadvantages:
      • Overhead software routines needed for blocking and record-keeping
      • Waste of buffer space

    Direct Access Storage Devices

    • Random access storage devices: read and/or write directly to specific areas.
      • E.g., magnetic disks, optical discs, solid-state memory
    • Access time variance:
      • Access time depends on where a data record is located on the device
    • Magnetic Disk Storage:
      • Concentric, number tracks from outside-in
      • Read/write heads move in unison
    • Accessing records: - Needs cylinder number, surface number, and sector number.

    Access Times

    • File Access Time Factors:
      • Seek time (moving the read/write head)
      • Rotational delay (waiting for the desired data to rotate to the read/write head)
      • Search time involved in determining where the record is located is critical to speed and efficiency
      • Transfer time (actually reading/writing the data)

    Fixed-Head Magnetic Drives

    • Record access with track number and record number
    • Total access time search time + transfer time
    • Three basic positions for requested records relative to read/write head position
    • Blocking minimizes access time.

    Movable-Head Magnetic Disk Drives

    • Access time seek + search + transfer time
    • Strategies use calculations for seek and transfer time.

    Device Handler Seek Strategies

    • Methods (e.g., first-come, first-served (FCFS), shortest seek time first (SSTF), SCAN, C-SCAN, LOOK) that define seek order.
    • Goal minimizes seek time, arm movement, mean response time.
    • Methods include:
      • FCFS
      • SSTF
      • SCAN
      • LOOK
      • N-Step SCAN
      • C-SCAN
      • C-LOOK

    Optical Disc Storage

    • Design Features:
      • Single spiral track, concentric tracks
      • Same sized sectors
      • Constant linear velocity (CLV)
    • Performance Measures:
      • Data transfer rate (Mbps): speed of reading large data amounts
      • Average access time: time needed to locate and access a random data item.
    • Additional features:
      • Data recorded/retrieved consistently
      • Data storage in sectors
      • Two-sided/single-sided storage

    CD and DVD Technology

    • Data recording: zeros and ones, pits, and lands, light striking land reflects to photodetector
    • Reads with low-power laser.
    • Light strikes land: reflected light to photodetector
    • Light strikes pit: scattered and absorbed light
    • Photodetector: converts light intensity into digital signal.
    • CD-R: write-once technology, requires expensive controller
    • DVD: several discs with greater capacity
    • Rewritable disks use phase-change technology.

    Solid State Storage

    • Implements Fowler-Nordheim tunneling phenomenon.
    • Stores electrons in floating gate transistor.
    • Electrons remain after power off.
    • Typical in flash memory storage.

    Flash Memory Storage

    • Electrically erasable, programmable, read-only memory (EEPROM).
    • Data written as electric charge sent through floating gate.
    • Erasing data uses a strong electrical field.

    Solid State Drives

    • Fast storage devices (expensive)
    • Typical device functions in smaller physical space than magnetic drives.
    • Work electronically; no moving parts.
    • Require less power—silent, and relatively lightweight.
    • Disadvantages: disastrous crashes, data degradation over time.

    Components of the I/O Subsystem

    • Input/output channels
    • Programmable units
    • Located between CPU and control unit
    • Synchronizing device speeds (CPU with I/O device)
    • Managing concurrent CPU and I/O device requests for faster processing; handles overlap.
    • Input/output control unit
    • Input/output channel program
    • Disk controller
    • Input/output subsystems

    Communication Among Devices

    • Resolves problems in communication among devices.
    • Hardware flag tested by CPU, channel status word (CSW) contains flag and three bits in flag represent I/O system component.
    • Communication links between channels, control units, and devices
    • Speed disparities between CPU and I/O, handled by buffers.
    • Direct memory access (DMA) allows control units to access main memory directly without CPU intervention.
    • Double buffering improves data flow between slow I/O devices and fast CPUs.
    • Multiple paths increase flexibility and reliability.

    RAID

    • RAID levels provide different degrees of redundancy.
    • RAID 0: data striping, non-critical, devices appear as one logical unit.
    • RAID 1: mirroring (backup), expensive.
    • RAID 2: small strips, expensive, Hamming code.
    • RAID 3: striping, parity bit, one disk for redundancy.
    • RAID 4: simple scheme, computes parity, parity and data stored in different strips.
    • RAID 5: data striping and parity are distributed across multiple disks.
    • RAID 6: provides redundancy, requires two parity bits.
    • Nested RAID Levels: combine different levels.

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    Device Management Chapter 7 PDF

    Description

    This quiz covers various types of devices including dedicated, shared, and virtual devices, and compares their functionality and efficiency. It also delves into input/output (I/O) performance enhancements through blocking and buffering and explores RAID levels. Learn about different seek strategies and their impact on device access times.

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