A Floppy disk drive is a storage device, used to store data on floppy disks. The capacity of floppy disks to store data is low as compared to a hard disk drive or SSD. The FDD is not used in the latest desktop home computers but it is still used in some older industrial machines.
Sizes and Capacity of Floppy Disks used in FDDs
The floppy disk drive comes in two sizes with varying capacities.
- 5″ Floppy Disk Drive. Latest of the two sizes, this FDD supports the floppy disks of capacities 720Kb and 1.44Mb
- 5.2″ Floppy Disk Drive. The 5.25 Inches of FDD is the oldest model of the two and the floppy disks of 360Kb and 1.22Mb capacities can be used .
Floppy Disk Drive Connection in Computer
- 34-pin male connector on Motherboard. As you can see in the figure below, there is a 34 pin male connector on the motherboard which is assigned for floppy disk drive connection.
- FDD interface Cable. A 34-pin cable is required for connectivity to the floppy disk drive. With one cable you can connect two floppy disk drives. The Drive that connects at the twisted end becomes A-Drive and the drive at the other end turns into B-Drive.
“TIP: The red wire is the No.1 wire and makes sure to connect it to the No.1 of connectors on both FDD and motherboard”
“Warning: If the LED on the front side of FDD glows permanently it means the cable is connected in reverse direction.”
- Power Connector. The power is supplied to FDD on a 4-pin male connector as shown in the figure.
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Motors used in Floppy Disk Drive
- Spindle Motor. It is used for media rotation that is to rotate the floppy disk at the speed of 360 RPM(rotation per minute) for 1.22 Mb floppies and at the speed of 300 RPM for 1.44Mb.
- Stepper Motor. There are two heads to read media. The media(floppy disk) rests between Head 0 and Head 1. The stepper motor is used for the movement of the head. The stepper motor needs step pulse signal and direction signal which it receives from FDD-controller chip on the motherboard.
- Head 0. As you can see in the picture, this head is stationary and cannot move and is fixed on the lower portion of FDD.
- Head 1. Out of the two heads, it is Head 1 that moves forward and backwards and is mounted on the upper portion of FDD.
Floppy Disk Geometry Table
| Capacity | Sides | Tracks | Sectors / Track | Bytes / Sector | Tracks/Inch(TPI) |
| 360 Kb | 2 | 40 | 9 | 512 | 48 |
| 1.2 Mb | 2 | 80 | 15 | 512 | 96 |
| 720 Kb | 2 | 80 | 9 | 512 | 135 |
| 1.44 Mb | 2 | 80 | 18 | 512 | 135 |
Calculating floppy disk capacity
Note: 360 bytes=0.3 Kbytes
Calculation of disk capacity ( in Kbytes)= No. of Sides x No. of Tracks x Sectors/track x Kbytes/sector
Example- 720Kb: 2 x 80 x 9 x 0.512=720Kb (values taken from above Table)
Different types of sensors in Floppy Disk Drive
- Media Sensor. Media sensor is used to detect whether the floppy is inside the drive or out. For earlier disks size of 5.25 Inches, this sensor is of optical type and the floppy disks with 3.5 inches of size, the same sensor works on magnetic principle.
- Track 0 Sensor.Whenever the head touches the first track that is track 0, this optical sensor gets activated.
- Index Hole Sensor. If the light manages to get passed through this small hole, it means the head has moved to the next track. The Index Hole sensor then the status signal to the electronics controller chip.
- Write Protect Sensor. Write Sensor is used to enable or disable writing the data on floppy. If the sensor is ON, you can write data and prevents writing if this sensor is in Off position.
I like your article, but wanted to add that that the old 51/4″ drives had an edge connector rather than the pin connector shown in your pic. They also sported a jumper select for in the event that you had two floppy’s you could determine (M)aster (S), or (CS) for cable select. Keep those drives. if you ever come across an old floppy you need to read, better to have one and not need it… I do not see too many rigs rocking the five and a quarter drive:)