Floppy disk drives were a key computer component for 20 years.
If you have spent any time at all working with a computer,
then chances are good that you have used a floppy disk at
some point. The floppy disk drive (FDD) was the primary means
of adding data to a computer until the CD-ROM drive became
popular. In fact, FDDs have been a key component of most personal
computers for more than 20 years.Basically,
a floppy disk drive reads and writes data to a small, circular
piece of metal-coated plastic similar to audio cassette tape.
of the Floppy Disk Drive
The floppy disk drive (FDD) was invented at IBM by Alan Shugart
in 1967. The first floppy drives used an 8-inch disk (later
called a "diskette" as it got smaller), which evolved
into the 5.25-inch disk that was used on the first IBM Personal
Computer in August 1981. The 5.25-inch disk held 360 kilobytes
compared to the 1.44 megabyte capacity of today's 3.5-inch
diskette. The 5.25-inch disks were dubbed "floppy"
because the diskette packaging was a very flexible plastic
envelope, unlike the rigid case used to hold today's 3.5-inch
the mid-1980s, the improved designs of the read/write heads,
along with improvements in the magnetic recording media, led
to the less-flexible, 3.5-inch, 1.44-megabyte (MB) capacity
FDD in use today. For a few years, computers had both FDD
sizes (3.5-inch and 5.25-inch). But by the mid-1990s, the
5.25-inch version had fallen out of popularity, partly because
the diskette's recording surface could easily become contaminated
by fingerprints through the open access area.
Data on a Floppy Disk
The following is an overview of how a floppy disk drive writes
data to a floppy disk. Reading data is very similar.
The computer program passes an instruction to the computer
hardware to write a data file on a floppy disk, which is very
similar to a single platter in a hard disk drive except that
it is spinning much slower, with far less capacity and slower
computer hardware and the floppy-disk-drive controller start
the motor in the diskette drive to spin the floppy disk. The
disk has many concentric tracks on each side. Each track is
divided into smaller segments called sectors, like slices
of a pie.
A second motor, called a stepper motor, rotates a worm-gear
shaft (a miniature version of the worm gear in a bench-top
vise) in minute increments that match the spacing between
The time it takes to get to the correct track is called "access
time." This stepping action (partial revolutions) of
the stepper motor moves the read/write heads like the jaws
of a bench-top vise. The floppy-disk-drive electronics know
how many steps the motor has to turn to move the read/write
heads to the correct track.
The read/write heads stop at the track. The read head checks
the prewritten address on the formatted diskette to be sure
it is using the correct side of the diskette and is at the
proper track. This operation is very similar to the way a
record player automatically goes to a certain groove on a
the data from the program is written to the diskette, an erase
coil (on the same read/write head assembly) is energized to
"clear" a wide, "clean slate" sector prior
to writing the sector data with the write head. The erased
sector is wider than the written sector -- this way, no signals
from sectors in adjacent tracks will interfere with the sector
in the track being written.
Disk Drive Facts
Here are some interesting things to note about FDDs:
Two floppy disks do not get corrupted if they are stored together,
due to the low level of magnetism in each one.
your PC, there is a twist in the FDD data-ribbon cable --
this twist tells the computer whether the drive is an A-drive
or a B-drive.
many household appliances, there are really no serviceable
parts in today's FDDs. This is because the cost of a new drive
is considerably less than the hourly rate typically charged
to disassemble and repair a drive.
you wish to redisplay the data on a diskette drive after changing
a diskette, you can simply tap the F5 key (in most Windows
the corner of every 3.5-inch diskette, there is a small slider.
If you uncover the hole by moving the slider, you have protected
the data on the diskette from being written over or erased.