b_book1.gif (162 bytes)Secondary storage
Use | Features | Compatibility | Data transfer rates
b_html2.gif (189 bytes)Care (Handling) | Formatting & write permit/protect | Zip Disk/Drive | Physical data organisation | Other uses - Sony

Floppy disks

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  •   Mylar plastic flexible disk coated with iron oxide coating, in an unsealed, flexible (5.25") or hard (3.5") plastic jacket.

  • 3.5" floppy diskettes are the most common type of storage on a Micro-Computer.
  • Examples;
    • Floppy (or Microfloppy) diskettes
      • Typical capacity(1998): 1.44MB
    • SuperDisk (LS-120)
    • Zip disk
      • Typical capacity(1998): 100MB

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Use

Features

  • Floppy disks gain rigidity when rotated at speed therefore mimic hard disks closely.
  • Removable
  • Cheaper than Hard disks and easy to handle
  • Transportable (Though removable Disks such as Iomega Zip or LS-120 disks becoming popular)
  • Less reliable than Hard Disks

Technical features


3.5" (micro)floppy disks (usually 1.44 Mbytes) - DSHD - most common


5.25" floppy disks (usually 1.2MBytes) DSDD

  • Flexible mylar diskette coated with iron oxide.
  • Capacity.
    • 3.5"
      DS/DD 720 KBytes
      DS/HD 1.44 MB
      DS/QD 2.88 MB
    • 5.25" DS/DD 360 KB - DS/HD 1.2 Mbyte
    • Iomega Zip disk 100 MB
    • LS-120 "Superdisk" (introduced 1997) 120MB.
  • Performance
    • 3.5
      • 25 millisec access time and data transfer rate of 500 Kbits / sec.
      • Spin at 300 rpm (one revolution in about .2 seconds)
      • Heads move from the center to the outside edge in about 0.17 sec.
      • maximum access time 0.2 sec (larger of the two)
      • Latency (bringing the disk up to speed) can give an access time of 0.5 seconds from a full stop.
  • Sides : Double sided
    Density : double, high, or quad (high) density
  • Physical organisation:
    Data and programs are stored in tracks and sectors where each sector is directly addressable giving fast access.

Compatibility

For 3.5" Microfloppies
  • Both IBM (and Compatible's) and Apple computers may come with 3.5" Micro-floppies.
  • Watch when taking IBM formatted floppies to an Apple as on older Apple computers in normal 'Apple' mode, the Apple Operating system will indicate the disk format is invalid and reformat for you!
  • The Apple "Super-drive" (introduced mid-1993) will accept both Macintosh and IBM DOS format disks.

For 5.25" Diskettes
  • Problems used to occur when taking disks from a 360K drive to a 1.2MB drive.

Data transfer rates

Drive size Diskette capacity Drive Capacity Transfer rates
3.5 720KB 720KB 250Kbs
1.44MB 250Kbs
(Reading a 720KB disk in a 1.44MB drive)
1.44MB 1.44MB 500Kbs
5.25 360KB 360KB 250Kbs
1.2MB 1.2MB 500Kbs
360KB 300Kbs

Kbs = Kilobits per second.

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[Rev: 19/7/98] 6-May-97 © 1997-98 V/2-Com (Verhaart), P O Box 8415, Havelock North, New Zealand.