A soft magnetic disk. It is called floppy because it flops if you wave it (at least, the 5¼-inch variety does). Unlike most hard disks, floppy disks (often called floppies or diskettes) are portable, because you can remove them from a disk drive. Disk drives for floppy disks are called floppy drives. Floppy disks are slower to access than hard disks and have less storage capacity, but they are much less expensive. And most importantly, they are portable.
Floppies come in two basic sizes:
b) Double sided High Density (DSHD or 25HD): It stores 1.2 Mbytes of data
b) Double sided High Density (DSHD or 25 HD): It stores 1.44Mbytes of data.
Floppies come in two basic sizes:
- 5¼-inch(Minifloppy disks): There are two types of 5.25 inch disk.
b) Double sided High Density (DSHD or 25HD): It stores 1.2 Mbytes of data
- 3.5 inch disk (Microfloppy) : There are two types of 3.5 inch disks.
b) Double sided High Density (DSHD or 25 HD): It stores 1.44Mbytes of data.
Definitions of some terms used above:
- When only one side of a disk is used to store information, it is called single sided.
- When both sides of a disk are used to store information, it is called double sided.
- When a disk stores information per unit length of a track, it is called Single density disk.
- When a disk stores doubles information per unit length of a track compared to a single density, it is known as double density disk.
5.25 inch Disk | 3.5 Disk | |||
Comparing Parameters | Double Density | High Density | Double Density | High Density |
Capacity | 360 KB | 1.2MB | 720KB | 1.44MB |
Tracks per surface | 40 | 80 | 80 | 80 |
Sector per track | 9 | 15 | 9 | 18 |
Disk capacity determination
The capacity of any disk can be calculated using the relation:
Disk capacity = NT Í NS Í NB Í S
Where,
Where,
NT : No. of tracks per surface of disk.
NS : No. of Sectors per track
NB : No. of Bytes per sector.
S : No. of Sides of the disk.
Ex-1: Find the capacity of a 5.25-inch double-sided double density disk (dsdd or 2S2 D)
Since, the 5.25 inch DSDD disk has: (See the above table)
No. of Tracks per surface (NT) =40
No. Sector per track (NS) =9
No. of Bytes per sector (NB) =512
No. of Sides (S) =2
Therefore, Disk capacity =NT Í NS Í NB Í S = 40 Í 9 Í 512 Í 2
No. Sector per track (NS) =9
No. of Bytes per sector (NB) =512
No. of Sides (S) =2
Therefore, Disk capacity =NT Í NS Í NB Í S = 40 Í 9 Í 512 Í 2
= 368640 Bytes
= 360Kbytes
Ex-2: Find the capacity of a 3.5 inch double sided double density (DSDD) disk.
Since, a 3.5 inch DSDD disk has (See above table)
No. of Tracks per surface (NT) = 80
No. Sector per track (NS) = 9
No. of Bytes per sector (NB) = 512
No. of Sides (S) = 2
Therefore, Disk capacity = NT Í NS Í NB Í S = 80 Í 9 Í 512 Í 2
= 737280 Bytes
= 720KBytes
Ex-3: Find the capacity of a 5.25-inch double-sided High Density (DSHD) disk.
Since, a 3.5-inch DSHD disk has (See above table)
No. of Tracks per surface (NT) = 80
No. Sector per track (NS) = 15
No. of Bytes per sector (NB) = 512
No. of Sides (S) = 2
Therefore, Disk capacity = NT Í NS Í NB Í S = 80 Í 15 Í 512 Í 2
= 1228800 Bytes
= 1200 Kbytes
= 1.2 Mbytes
Ex-4: What is the capacity of a DSHD disk of 3.5 inch?
Since, a 3.5 inch DSHD disk has (See above table)
No. of Tracks per surface (NT) = 80
No. Sector per track (NS) = 18
No. of Bytes per sector (NB) = 512
No. of Sides (S) = 2
Therefore, Disk capacity = NT Í NS Í NB Í S = 80 Í 18 Í 512 Í 2
No. of Bytes per sector (NB) = 512
No. of Sides (S) = 2
Therefore, Disk capacity = NT Í NS Í NB Í S = 80 Í 18 Í 512 Í 2
= 1474560 Bytes
= 1440 Kbytes
= 1.44 MBytes
Advantage of floppy disks compared with magnetic tape
- Random-access processing is possible.
- Quick and direct inquiry to records is possible.
Disadvantage of floppy disks
- Disk packs are more expensive than tape (for the same storages capacity).
- The sequential processing using disks may be slower and less efficient than sequential processing using tapes.
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