Floppy disks, also known as floppy discs ( FD), are exchangeable magnetic data carriers that ensure random access to data. They are plastic disks housed in rectangular floppy disk cases for contact protection and covered on one or both sides with a magnetizable layer. Data is stored on the layers in concentric tracks by magnetization. For this purpose, the diskette rotates at 360 rpm under the read/write head.
The development of floppy disks
Historically, the earlier 8" floppy disk, the standard floppy disk, was later replaced by the 5.25" floppy disk, the mini floppy disk, and this in turn by the 3.5" version, the micro floppy disk. The reduction in size and the simultaneous increase in storage capacity were due to improved magnetizable materials and thus to the higher storage density.
Thus, the rather large 8" floppy disk had between 180 kilobytes( KB) and 1.2 megabytes( MB) of storage capacity, the 5.25" floppy disk had 160 kB, 360 KB and 1.2 MB, and the 3.5" floppy disk had 720 KB (double density), 1.44 MB ( HD) and 2.88 MB (EHD). Other floppy disk formats, such as the 2.0", 2.5", 2.8", 3.0", 3.25" and the 4.0" floppy disks have not caught on.
The floppy disks contain some markings, such as the index hole, which marks the area and the beginning of the first sector, the write protection notch, which can be sealed for the 5.25" floppy disk and locked for the 3.5" floppy disk and as a further marking the HD marking, at which the floppy disk drive scans whether it is a Double Density( DD) or a High Density (HD) floppy disk with 1.44 MB.
Data is stored on concentric circular tracks in which the tracks are stored. The tracks are in turn divided into sectors. Between the tracks there are non-magnetic areas for track differentiation. The 5.25" diskette is available with 40 and 80 tracks and 9 or 15 (1.2 MB) sectors, the 3.5" diskette with 80 tracks and 9 or 18 (HD) sectors, which corresponds to a maximum total number of 2,880 sectors and ultimately leads to a storage capacity of 1.44 MB with a sector size of 512 bytes.
Since the storage space on the 3.5" floppy disk was not sufficient for many applications, various floppy disk systems with much higher storage capacities were developed, the super floppy disks. One system is the ZIP drives developed by Iomega, whose ZIP disks offer storage space for 100 MB and 250 MB. Another system that is backwards compatible with the 3.5" format is the LS-120 floppy disk with 120 MB storage capacity. Super floppies are available up to storage capacities of 1.5 GB (Syquest SyJet).