1.44 megabyte floppy disk drives using 3.5 inch diskettes have been around for about 15 years. At the time of their introduction they seemed like a miracle -- they were smaller than the standard 5.25 inch disks but they held more data!

Here are some of the parameters that determine how much data a floppy disk can hold:

  • Tracks per inch: 135
  • Total tracks per side: 80
  • Sectors per track: 18
  • bytes per sector: 512
  • Spin rate: 360 RPMs
  • head movement mechanism: worm gear and stepper motor
Two important things to notice are the low number of tracks on the disk and the fixed number of sectors per track. Neither one of these techniques makes very good use of the surface of the disk.

The main thing that separates a Zip disk from a floppy disk is the magnetic coating used on the disk. On a Zip disk the coating is much higher quality (see How Tape Recorders Work for some discussion on magnetic coatings). The higher quality coating means that a Zip disk read/write head can be significantly smaller than a floppy disk's (by a factor of 10 or so). The smaller head (and a head positioning mechanism similar to that used in a hard disk) means that a Zip drive can pack thousands of tracks per inch on the track surface. Zip drives also use a variable number of sectors per track to make the best use of disk space. All of these things combine to create a floppy disk that holds a huge amount of data!

Here are several of the patents that describe the Zip drive: