By Bradley Dunn,2014-11-12 07:45
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    Copyright: Louise Henry at GSU - CS

    Chapter 7: Storage

    Memory Versus Storage

    What is storage?

    ; Media and devices used to store and retrieve data, instructions, and information How does storage differ from memory?

    ; (Memory is also called primary storage or RAM)

    ; Storage (also called secondary storage):

    ; Stores items for future use, rather than temporarily

    ; Storage is nonvolatile, rather than volatile

    ; When you want to work with a file, you read it from storage and place it in memory ; When you are finished with the file, you write it from memory into storage How does volatility compare?

    ; Screen display and contents of most RAM (memory) erased when power is off ; Contents of storage retained when power is off

    What is a storage device and a storage medium?

    ; Storage device

    o Hardware that records and retrieves items to and from a storage medium ; Storage medium

    o Physical material on which a computer keeps data, instructions, and information What is reading and writing?

    ; Reading

    o Process of transferring data, instructions, and information from a storage medium into


    o Serves as a source of input

    ; Writing

    o Process of transferring items from memory to a storage medium

    o Serves as a source of output

    What is access time?

    ; Amount of time it takes device to locate item on disk

    ; Defines speed of disk storage device

    o Tape (slowest, least expensive)

    o Floppy Disk

    o Compact Disc

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    o Hard Disk

    What is capacity?

    ; Number of bytes (characters) storage medium can hold

    o Kilobyte KB 1 thousand

    o Megabyte MD 1 million

    o Gigabyte GB 1 billion

    o Terabyte TB 1 trillion

    o Petabyte PB 1 quadrillion

    Floppy Disks

    What is a floppy disk?

    ; Portable, inexpensive storage medium

    ; Today’s standard disk is 3.5” wide

    ; HD (High Density disk) Stores 1.44MB

    What are the parts of a floppy disk?

    ; Thin, circular, flexible film enclosed between two liners How are floppy disk drives designated?

    ; One floppy drive

    o drive A

    ; Two floppy drives

    o drive A

    o drive B

    How does a floppy disk drive work?

    ; 1: Shutter moves to expose recording surface on disk ; 2: Signal sent to control movement of read/write heads and disk ; 3: If write instruction, circuit board verifies whether disk can be written to

    ; 4: Motor causes floppy disk to spin

    ; 5: Motor positions read/write heads over correct location on disk ; 6: Read/write heads read data from or write data on the floppy disk What are tracks and sectors?

    ; Track is narrow recording band that forms full circle on disk surface ; Sector can store up to 512 bytes of data

    o 80 tracks per side X 18 sectors per track X 2 sides per disk X 512 bytes per sector =

    1,474,560 bytes = 1.44 MB

    What is formatting?

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; Process of preparing disk for reading and writing

    ; Formatting marks bad sectors as unusable

    How do you care for a floppy?

    ; Proper care helps maximize disk’s life

    ; Floppy disk can last at least seven years

    o Never open the shutter and touch the disk’s recording surface

    o Avoid exposure to heat and cold

    o Avoid exposure to magnetic fields

    o Avoid exposure to contaminants such as dust, smoke, or salt air

    o Keep disks in a storage tray when not using them What is a write-protect notch?

    ; Small opening with a cover that you slide

    ; Protects floppy disks from being erased accidentally

    o notch open means you cannot write on the disk

    o notch closed means you can write on the disk

    High-Capacity Disks

    What is a high-capacity disk drive?

    ; Uses disks with capacities of 100 MB and greater

    ; Primarily used to backup files and transfer files

    o Zip? drive

    o Uses a Zip? disk that can store 100 MB or 250 MB of data What is a backup?

    ; Duplicate of file, program, or disk that you can use if original is lost, damaged, or destroyed

    Hard Disks

    What is a hard disk?

    ; High-capacity storage (20 100 GB)

    ; Consists of several inflexible, circular platters that store items electronically

    ; Components enclosed in airtight, sealed case for protection How does a hard disk work?

    ; 1: Circuit board controls movement of head activator and small motor ; 2: Small motor spins platters

    ; 3: When software requests disk access, read/write heads determine location of data

    ; 4: Head actuator positions read/write head arms over correct location on platters to read or write data

    What is a cylinder?

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; Location of a single track through all platters

    ; Single movement of read/write head arms can read same track on all platters What is a head crash?

    ; Occurs when read/write head touches platter surface

    ; Spinning creates cushion of air that floats read/write head above platter

    o clearance between head and platter is approximately two millionths of an inch

    o gap is half the diameter of a dust particle

    What is a disk cache?

    ; Portion of memory processor uses to store frequently accessed items What is a partition?

    ; Formatted hard disk divided into separate areas called partitions ; Each partition functions as if it were a separate hard disk drive ; Designation for first partition or for a single partition on hard disk

    o drive C

    ; Designation for second partition on hard disk

    o drive D

    What is a removable hard disk?

    ; Disk drive in which a plastic or metal case surrounds the hard disk so you can remove it from the


    ; Used for backup or to transfer files

    How does RAID work?

    ; Disk system that duplicates data, instructions, and information to improve data reliability ensuring

    that data is not lost if one drive fails

    o Mirroring has one backup disk for each disk

    o Striping stores data across multiple disks

    What Windows utilities maintain a hard disk drive?

    ; Backup

    ; Disk Cleanup

    ; Disk Defragmenter

    ; Scheduled Tasks

    What is an Internet hard drive?

    ; Service on Web that provides storage to computer users

    o Most offer free storage

    o Revenues come from advertisers

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What are advantages of an Internet hard drive?

    ; Large audio, video, and graphics files can be downloaded to an Internet hard drive instantaneously

    ; Files can be accessed from any computer or device with Web access ; Others can be authorized to access data from your Internet hard drive ; Allows offsite backups of data

    Compact Discs

    What is a compact disc (CD)?

    ; Storage medium

    ; Most PCs include some type of compact disc drive ; Available in variety of formats

    o CD-ROM

    o CD-R

    o CD-RW

    o DVD-ROM

    ; DVD+RW

    How do you use a compact disc?

    ; CD drives can read compact discs, including audio discs How does a laser read data on a compact disc?