How a Computer Works (2015)
20. Floppy Drive
Floppy Drive
Floppy Disk
Originally the floppy disk was the primary means of transferring files to your computer. Today CD-ROM and DVD has largely superseded it. The storage capacity of a Windows formatted floppy disk is 1.44 megabytes, which is tiny, compared to the 650 megabytes a CD-ROM will hold. Hence today most software programs come on CD-ROM, as using floppy disks would require a lot of disks.
3.5 inch disk
The floppy disk drive uses a 3.5-inch disk. The 3.5-inch floppy disk is enclosed in a protective plastic housing. The disk substrate is a thin Mylar plastic coated on both sides with a magnetic material. The disk can be write-protected so data cannot overwrite existing data. A small flap is moved to write protect the disk. The disk is double sided and data is written on both sides.
Formatting
Before the disk can accept data it must be formatted. Formatting creates tracks and sectors that allow data to be organized and managed by the drive.
Tracks are arranged in concentric rings that are divided into sectors. Data written into these sectors are called clusters.
A directory stores information on what files are on the disk and their respective locations. Existing data can be erased or written over.
Inside the drive
Disk in drive shows disk surface
Inserting the floppy disk into the drive presses the disk against a system of levers. One lever opens the metal shutter on the outside of the disk casing.
This action enables the drives read/write heads to come close to the disk surfaces. The read/write heads are located on both sides of the disk surfaces.
The heads move together but are not directly aligned to each other; this prevents interaction between write operations on the two disk surfaces.
Read/Write
Reading and writing data is done through the same head; a second, wider head is used for erasing a track before it's written on. Underneath the disk is a small electric motor. The motors spindle goes through the centre of the disk.
When reading or writing data the motor spins the disk at either 300 or 360 rotations per minute.
A stepper motor fastened to the read/write heads moves them to the right track position.
Controller
The floppy disk drive controller starts the motor to spin the disk and switches on the led indicator on the outside of the drive.
When the drive receives data from the computer the drive checks whether light is visible through a small hole in the disk casing.
If light is detected from a light emitting diode shining through the hole, the drive knows the disk is write protected and refuses to write data to the disk.
Moving the heads
Otherwise a second motor rotates a worm gear shaft connected to the read/write heads. This movement is carefully controlled by the drives electronics so the heads are over the right track. Before data is written an erase coil on the heads is energized to clear a wide sector prior to writing data.
Inside the heads are electromagnets, which create magnetic pulses when, energized. These pulses change the polarity of magnetic pulses in the disks coating.
Writing data
Disk inserted
Head moved to read data
Data being read
Finally to write the data the stepper motor moves the drives head across the disk surface and writes data to the disk. The magnetized particles on the disk surface have their north and south poles orientated in such a way that their pattern may be detected and read when data is read from the disk.
The disk controller updates the disk directory with information on what files are on the disk and their respective locations and switches off the led indicator.