Floppy%20Drives

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Chapter 7

• Floppy Drives

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Floppy Drives

• 3.5 inch 1.44 Mbytes
• Usages
• Data transfer
• Small file backup
• Software distribution, e.g., device drivers

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Floppy Drive Subsystem
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How Data Is Physically Stored on a Floppy Disk

• In concentric circles (tracks or cylinders)
• Each track is divided into sectors
• Each sector holds 512 bytes of data

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How Data Is Physically Stored on a Floppy Disk
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Floppy Disk

• Each bit is a magnetized, rectangular spot
• Two read/write heads
• Head actuator physically positions the
  read/write heads over the correct track
• Spindle motor spins the floppy disk
• Tunnel-erase heads erase any stray magnetic
  information recorded outside the defined track it
  is writing

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Inside a Floppy Disk Drive
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How Data Is Physically Stored on a Floppy Disk
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Formatting a Floppy Disk

• Low-level formatting recording the tracks and
  marking the start of each sector on each track
• High-level formatting creating the disk's
  logical structures such as the file allocation
  table and root directory

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Ways to Format a Floppy Disk

• Format command from a command prompt
• Windows Explorer, right-click the 3½ Floppy (A)
  icon and select Format on shortcut menu

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3.5 inch Floppy Disk Geometry

• 2 sides
• 80 tracks/side
• 18 sectors/track
• 512 bytes/sector
• Storage capacity

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How Data Is Logically Stored on a Floppy Disk

• Cluster
• Smallest logical unit of space allocated and
  accessed by the operating system
• On a 3½-inch high-density floppy disk, one
  cluster one sector (512 bytes)

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Project 1 Data are Allocated in Clusters?

• Insert a floppy disk, check its space usage
• Create a file with only one letter and save it to
  the floppy disk
• Check the space usage again

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High-level Formatting of a Floppy

• Creates boot record
• Creates two copies of file allocation table (FAT)
• Creates root directory

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Boot Record

• First sector of the disk (track 0, sector 1
  (bottom of the disk, outermost track))
• Stores basic information about how the disk is
  organized
• Has a bootstrap loader that can be used to boot
  from the disk

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File Allocation Table (FAT 12)

• One-column table
• Width of each entry in the column is 12 bits
• Records
• Location of the next file cluster
• Unused/Bad status

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Root Directory Table

• A table with a fixed number of entries, each for
  a file or a subdirectory under the root directory
• Each entry
• File name and extension
• Time and date of last update
• File size
• File attributes
• Starting cluster

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How the OS Uses the FAT and Directory Table
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Common Error Messages

• Non-system disk or disk error. Replace and strike
  any key when ready.No operating system found.
• Bad or missing COMMAND.COMError in Config.sys
  line xxHimem.sys not loadedMissing or corrupt
  Himem.sys

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Common Error Messages

• Invalid Drive Specification
• Not ready reading drive A, Abort, Retry, Fail?
• General failure reading drive A, Abort, Retry,
  Fail?
• Track 0 bad, disk not usable
• Write-protect error writing drive A

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Project 2 Replacing a Floppy Drive

1. Check that computer and other peripherals are
   working
2. Turn off computer and remove cover
3. Unplug data cable and power cable from old drive
   unscrew and dismount the drive
4. Slide new drive into the bay reconnect data
   cable and power cable
5. Turn on computer check setup test the drive
   turn off computer and replace the cover