Floppy Drive

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Floppy Drive
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Start with a non-magnetic platter.
Floppy Disk - Mylar Hard Disk - Metal, Ceramic,
or Glass
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Coat with a thin layer of magnetic material.
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Two important characteristics of the magnetic
surface

• Coercivity
• Retentivity

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Coercivity

• How strongly the material resists changing its
  magnetic field.
• Must be high enough to resist changes by
  unintentional means.
• Must be low enough so that excess write current
  is not required.
• Generally, larger drive capacities require higher
  coercivity.

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Retentivity

• How well the magnetic material retains its
  magnetic field.
• Relates to how long a magnetic material can
  retain data without degradation.

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Magnetic domains randomly arranged. (Blank media)
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Pick-up device - Read/Write Head
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Magnetic domains orderly arranged. (Recorded
Media)
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Reading Data from the Disk.
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Writing Data on a Blank Disk.
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The disk surface is divided into tracks.
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Side 1, Track 0
Side 2, Track 0
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Read\Write Head
Disk
Read\Write Head
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One Sector 512 Bytes
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SECTOR

• The smallest unit of storage on a disk.
• 512 bytes or 0.5 kbytes
• Grouped into clusters

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Most Hard Drives Have Multiple Platters.
Platter1, Track1
Platter2, Track1
Platter3, Track1
Platter4, Track1
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The eight track 1s are referred to collectively
as Cylinder 1.
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Read\Write Head
Platter
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Read\Write Head
Disk
Read/Write Head
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One Sector 512 Bytes
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Cluster
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Cluster

• The smallest unit of disk space that OS can
  allocate to a file.
• It consists of one or more sectors.
• Generally, the larger the disk drive the more
  sectors per cluster.

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File Allocation Table (FAT)

• OSs road map to the disk drive.
• How OS keeps track of which clusters belong to
  which files.
• How OS keeps track of bad sectors.
• Two copies maintained and kept up to date by OS.

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Formatting

• Low Level Formatting - Performed by the Disk
  Drive Manufacturer.
• High Level Formatting - Performed by the PC User
  via the FORMAT Command.

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Low-Level Formatting
Blank Disk
Sectors and tracks defined
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Low Level Formatting

• Performed at the factory.
• Converts the single blank surface into tracks and
  sectors.
• Finds and remaps bad spots on the disk so that
  the operating system can avoid them.

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High Level Formatting

• Originally performed by the vendor of the
  computer.
• Creates Boot Record, FAT, and the Root Directory.
• Performed with the FORMAT Command.

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Partitioning

• Makes the hard disk compatible with the operating
  system.
• Prepares the hard disk for high-level format.
• Divides the hard disk into two or more partitions
  or makes it all one large partition.
• Performed with the FDISK command.