How was data stored on floppy disks


Floppy disks, also known as floppy disks (FD), are exchangeable magnetic data carriers that guarantee random access to the data. These are plastic disks that are housed in rectangular disk sleeves for protection against accidental contact and are covered on one or both sides with a magnetizable layer. The data is stored on the layers by magnetization in concentric tracks. To do this, the disk rotates at 360 rpm under the read / write head.

The evolution of the floppy disks

Historically, the earlier 8 "diskette, the standard diskette, was later replaced by the 5.25" diskette, the mini-diskette, and this in turn by the 3.5 "version, the micro-diskette The reduction in dimensions and the simultaneous increase in storage capacity were due to improved magnetisable materials and thus to the higher storage density. The rather large 8 "floppy disk had between 180 kilobytes (KB) and 1.2 megabytes (MB) of storage capacity, the 5, 25 "diskette 160 kB, 360 KB and 1.2 MB and the 3.5" diskette 720 KB (double density), 1.44 MB (HD) and 2.88 MB (EHD). Other disk formats such as the 2.0 ", 2.5", 2.8 ", 3.0", 3.25 "and 4.0" 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 on the 5.25 "diskette and locked on the 3.5" diskette and as a further marking the HD identification on which the floppy disk drive scans whether it is a Double Density (DD) or a High Density (HD) 1.44 MB floppy disk.

The data is stored on concentric circular paths in which the tracks are stored. The tracks are again divided into sectors. There are non-magnetic areas between the tracks to distinguish between tracks. 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 is a maximum This corresponds to a total 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 insufficient for many applications, various floppy disk systems with significantly higher storage capacities, the super floppy disks, were developed. One system are the ZIP drives developed by Iomega, whose ZIP floppy disks have a storage capacity of 100 MB and 250MB. Another system that is backward compatible with the 3.5 "format is the LS-120 floppy disk with 120MB of storage capacity. Super floppies are available with storage capacities of up to 1.5 GB (Syquest SyJet).