1.  The Physical Contents of a Floppy Disk (3.5 inch)

• Consists of a circular, thin, flexible plastic disk with a magnetic coating enclosed in a square-shaped plastic shell
• Components: Shutter, Shell, Liner, Disk, Metal Hub, Magnetic Coating

picture adapted from: Discovering Computers 2000 (see below)

picture taken from: http://webclass.cqu.edu.au/Units/81120_FOCT_ Hardware/Study_Material/Study_Guide/chap3/sec1p1.html

2.  Characteristics of a Floppy Disk

• A "track" (see figure below) is a narrow recording band that forms a full circle on the surface of the disk
• The disk's storage locations are then divided into pie-shaped sections, which break the tracks into small arcs called sectors (can hold 512 bytes of data)
• Floppy Disks store data on both sides.  Each side consists of 80 tracks with 18 sectors per track
• To read from and write on the disk, sectors are grouped into clusters (consist of 2 to 8 sectors)
• A cluster is the smallest unit of space used to store data

picture adapted from: Discovering Computers 2000 (see below)

3.  How It Works

• Step 1: When you insert the floppy disk into the drive, the shutter moves to the side to expose the recording surface on the disk
• Step 2: When one initiates a disk access, the circuit board on the drive sends signal to control movement of the read/write heads and the disk
• Step 3: If disk access is a write instruction, the circuit board verifies that light is not visible through the write-protect notch
• Step 4: A motor causes the floppy disk to spin
• Step 5: A motor positions the read/write heads over the correct location on the recording surface of the disk
• Step 6: The read/write heads read data from and write data on the floppy disk

picture adapted from: Discovering Computers 2000 (see below)

5.  Advantages and Disadvantages

• Advantages: portable, inexpensive, write-protect notch
• Disadvantages: cannot hold a lot of information compared to other modes of storage, fairly easy to damage, relatively slow, sometimes not formatted (although not difficult to do)

• A typical High Density Floppy Disk contains 1.44 megabytes

7.  Cost Per Megabyte (assuming 1.44 MB)

picture taken from: http://cgl.microsoft.com/clipgallerylive/default.asp

• If purchased individually, usually cost about $1.00: $0.69 per megabyte
• If purchased in bulk, much cheaper (example: 50 disks for $19.99):  $0.28 per megabyte

This Is A Student Website

Last Edited On May 14, 2000

Information for this page based largely upon:
Shelly, Gary B., et al.  Discovering Computers
    2000: Concepts for a Connected World.
    Cambridge: Course Technology, 1999.