Floppy Drives, Optical Storage by pptfiles

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									                               Floppy Drives, Optical Storage
                            November 1 (Day); November 3 (Night)


   Introduction:
        o   The floppy drive has been a part of the personal computer since the start. It has
            moved from being 5 ¼ inch wide to its current width of 3 ½ inches (p. 179).
        o   Early PCs did not even have hard drives. All programs and data were read from and
            stored on floppy disks (p. 177).
        o   Most of the early PCs actually had two floppy drives. One was used to store the
            program. The other was used to store the data you were working on.




                                Old Computer with two Floppy Drives

   Floppy Drive Connections:
        o   A floppy drive controller is a small hardware device that is used to control the flow
            of data to and from RAM. Remember that all data on your computer must first go to
            RAM before it can be processed.
        o   In olden times, the floppy drive controller was an expansion card that actually
            plugged into an expansion slot. Today, a generic floppy drive controller is installed
            on all motherboards.


        o   Data Cables:
                       The floppy drive connects to its controller (whether it be on the
                        motherboard or controller card) by a 34-pin cable (p. 179).
                                Most floppy drive cables have one connector. Some have two
                                 (p. 179).
                                If you have two connectors, BIOS will recognize the floppy
                                 drive on the end of the cable as A: and the floppy drive installed
                                 on the second computer as B: (p. 179).




                  The Floppy Drive You Intend to be Drive A: Needs to Be on End


   Floppy drives receive power from the power supply through a Mini connector (p. 160).


   How Data is Physically Stored on a Floppy Drive:
       o   All floppy disks are coated with a metallic film capable of holding a magnetic charge.
           The magnetic coating on a newly made floppy disk has no charge until it is
           formatted, which happens before it leaves the factory (p. 177).
       o   Formatting is a process that places organizational information on the floppy disk so
           that it can store data in a useful way by placing magnetic charges on the disk (p. 177).
       o   More simply, formatting can be stated as the process of mapping tracks and sectors
           on the disk.
       o   Tracks are a series of circles. There are eighty tracks on the top and eighty tracks on
           the bottom of the disk.
       o   Each track is broken down into nine sectors. Each sector can be broken down into
           512 bytes (p. 177).




                                 Tracks and Sectors on a Floppy Disk
       o   Data is written to the disk as bits. Each bit is actually a small magnetized area on the
           disk with unmagnetized spots in between. These gaps prevent the magnetic field of
           one bit from corrupting the magnetism of a nearby bit.


   Disk Density:
       o   The smaller the unmagnetized areas, the more closely bits may be placed to one
           another and the more bits can be fit on a disk. This increases the disk density.
       o   Double-density means that the tracks are packed together twice as closely as tracks
           on a single-density disk (p. 179).
       o   Disk density is increased by using higher quality disk surfaces. The higher quality
           disk surfaces are less sensitive to magnetic fields. This means that bits may be
           placed closer together without being corrupted by the magnetic field of a nearby bit.

   Physical Connection of the Drive:
       o   Each floppy disk has two read/write heads: one for the top and one for the bottom of
           the disk.
                       The read/write heads move together. Therefore, the top read/write head
                        and the bottom read/write head will always be positioned in the same
                        place.
                       The read/write heads lightly touch the surface of the disk.
       o   Each floppy drive has a spring mechanism that pulls back the metal tab on the floppy
           disk, thus exposing the disk surface so that the read/write heads can make contact
           with the surface (p. 178).
       o   Each floppy drive has a motor-driven spindle that makes the disk spin (p. 178).

   CD-ROM drives and DVD drives are known as optical media.

   CD-ROM Drives:
       o   Here are some ways that the CD-ROM drive differs from the floppy drive:
                       Data can be written to a CD-ROM disc only once, because the surface of
                        the disc is actually embedded with data.
                       Instead of storing data in a series of tracks, the surface of the CD-ROM
                        disc is laid out in one continuous spiral patterns.
                       The surface of a CD-ROM stores data as pits and lands (p. 241):
                               Pits are recessed areas, or holes, on the disc surface and
                                represent a binary 0.
                               Lands are raised areas on the disc surface and represent a binary
                                1.




                                          Pits and Lands


                       Instead of using read/write heads, CD-ROM drives use a laser beam.
                        The laser beam distinguishes between a pit and a land by the way that
                        light is deflected when the beam hits the surface of the disc.


                       Link to Demonstration of How a CD Reads Data
                   at http://static.howstuffworks.com/flash/cd-read.swf


       o   The first CD-ROM drive transferred data at a rate of 150 KB/sec. This transfer rate
           was fine for audio CDs, but not good for data CDs. This speed of this first CD-ROM
           drive is known as 1X (p. 243).
                       The speeds listed for CD-ROMs today are simply multipliers of this first
                        CD-ROM drive speed. A 20X CD-ROM, for example, is twenty times
                        faster than the first CD-ROM drive.

   CD-R and CD-RW Drives:
       o   CD-Recordable (CD-R) drives allow data to be written to a disc and be read by all
           regular CD-ROM drives (p. 244).
                       CD-R drives apply heat to special chemicals on the disc that cause areas
                        on the disc that to reflect light differently than other areas. This process
                        is known as burning (p. 244).
                             Back of CD-Recordable Disc; It’s Not Silver


      o    CD-Rewritable (CD-RW) drives allow data to be added to a disc and then changed
           later (p. 246).
                       CD-RW uses a special chemical that crystallizes when the laser beam
                        strikes it and decrystallizes when higher heat is applied (p. 246).



   DVD:
      o    A DVD is capable of storing massive amounts of data. It takes 7 CDs to store a full-
           length movie, but only 1 DVD.
      o    CD and DVD share many similarities. Both use tiny pits and lands on their surface to
           represent bits, which are then readable by a laser beam. They are both 5 in. wide and
           1.2 mm thick.


      o    Here’s how CD and DVD drives differ:
                       The DVD drive uses a shorter wavelength laser, so it can read smaller,
                        more densely packed bits, which increases the disc’s capacity.
                       DVD discs can have two layers of bits, instead of one.
                       A DVD disc can use both the top and bottom of the disc.

								
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