Evolution of Storage Disks Part IV (5¼ inch floppy)

In our previous articles, we saw how the 8-inch floppy drives came into existence and its development in due course of time. As time passed by, people felt that the 8-inch floppies were really big for the desktops to use. And this led to the development of 5 ¼ inch disk. Its capacity was 98.5KB and then later increased to 110KB. In the year 1978, Apple introduced the 5¼ inch floppy disks called DISK II for the Apple II machines. Its size was 113 KB and later on increased to 140 KB in the year 1980.

In the late 1980’s, quad density disks were developed which abundantly increased the storage capacity to 720KB. This is almost 5 times greater than the previously used disks

. In the year 1984, came the high density disks with a storage capacity of almost 10 times more than the previous disks. This had a storage capacity of 1200 KB (1.2MB). These high density disks were identical to the double density disks except for their labels. In these situations the drive itself was unable to find the type of media used, and hence it was possible for a high density disk drive to format a double density disk to the higher capacity which resulted in bad sectors. This problem was due to the high-coercivity oxide coating on the disk which required strong magnetic field to write data onto it.

The double density disks required fewer magnetic fields for the writing purpose. In order to format or write to this high-coercivity media, the high-density drive switched its heads into a mode using a stronger magnetic field. When these stronger fields were written onto a double-density disk (having lower coercivity media), the strongly magnetized oxide particles would begin to affect the magnetic charge of adjacent particles. The net effect is that the disk would literally begin to erase itself. On the other hand, the opposite procedure (attempting to format an HD disk as DD) would fail almost every time, as the high-coercivity media would not retain data written by the low-power DD field. This problem was then overcome by the 3½ inch floppies.