Your lesson could begin with a short historical overview:
"History 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 diskettes.
By 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."
from:
( http://computer.howstuffworks.com/floppy-disk-drive1.htm )
The basic information on the storage medium disk is necessary to
understand the floppy disk drives function. Please read:
"Parts of a floppy disk drive - the disk"
"Parts of a floppy disk drive - the drive"
(both chapters on one page)
( http://computer.howstuffworks.com/floppy-disk-drive2.htm )
How the data is stored or read from the disk:
"Writing 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. Here's what happens:
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 access time.
The 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 tracks.
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 vinyl record.
Before 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.
The energized write head puts data on the diskette by magnetizing
minute, iron, bar-magnet particles embedded in the diskette surface,
very similar to the technology used in the mag stripe on the back of a
credit card. The magnetized particles have their north and south poles
oriented in such a way that their pattern may be detected and read on
a subsequent read operation.
The diskette stops spinning. The floppy disk drive waits for the next command."
from:
( http://computer.howstuffworks.com/floppy-disk-drive3.htm )
About the levers (and more):
"1. When you insert a 3.5-inch floppy disk into the floppy drive, it
presses against a system of levers. One lever opens the shutter to
open the cookie. The cookie is nothing you can eat. It is the mylar
disk coated on each side with a magnetic material that can store your
data.
2. Other levels and gears move two read/write heads until they almost
touch the cookie on either side. These heads are tiny electromagnets
and use magnetic pulses to change the polarity of metallic particles
embedded in the disk's coating.
3. The drive's circuit board receives signals, including data and
instructions for writing that data to disk, from the floppy drive's
controller board. The circuit board then translates the instructions
into signals that control the movement of the disk and the read/write
heads.
4. If the floppy disk you have inserted into the floppy drive is write
protected a small beam can't pass through the floppy drive it don't
write on your floppy drive.
5. A motor is located beneath the disk. It spins a shaft that engages
a notch on the hub of the disk, causing the disk to spin.
6. A stepper motor connected to a shaft that has a spiral groove cut
into it. An arm attached to the read/write heads rests inside the
shaft's groove. When the shaft turns, the arm moves back and forth,
positioning the read/write heads over the disk. "
7. When the heads have moved to the correct position, electrical
pulses create a magnetic field in one of the heads to write data to
either the top or bottom surface of the disk. When the heads are
reading data, they react to magnetic fields generated by the metallic
particles on the disk. "
( http://home.swipnet.se/~w-24488/floppy.html )
The data is not stored in sound or morse code, but in the basic
information unit of digital computer units - bits. Early computer
technology used paper tape to store the bits, mangetic data storage
uses the same basic idea of storing bits:
(There are more pictures in ths article)
"Paper Tape
One of the first methods of storing data and software for use on a
computer was the use of punched paper tape. The tape was fed through a
special tape reader and the rows of dots converted to numbers.
Punched cards were also used to store data. These were sometimes
punched by hand and had to be entered into the computer in the correct
order ... if you dropped the cards and they became disordered then you
may have had to start all over again.
Each dot corresponds to a BInary digiT (or BIT) of data. Eight bits in
a group are called a BYTE (some people refer to half a byte, or 4
bits, as a NYBBLE).
Magnetic Tape
The problem with paper tape was that it kept on breaking - since the
more holes that you punched in it the more fragile it became.
Another problem with paper tape was that the large size of the holes
on the paper meant that you needed very long lengths of tape to store
lots of data or small computer programs.
Magnetic tape works along the same principles as paper tape. However,
the tape is made of a thin film of plastic with a magnetic covering on
it. Instead of holes punched into the tape there were much smaller
areas of magnetised and non-magnetised tape.
This proved to be so successful that magnetic tape is still used today
- not as much in computing but the videotapes that you use to record
films on are made of the same material.
Magnetic tape had a problem though. Just like when you want to fast
forward to the end of the film you have to wait for the tape player to
wind on all the film ... the same thing happened if you wanted some
data at the end of the tape: you had to winf all the way through the
whole tape.
This was very time-consuming.
Magnetic (floppy) Disks
To solve the problem of magnetic tape - the two ends of the tape were
joined together to form a magnetic disk.
If you take an old, broken floppy disk apart you will find inside of
it a circular sheet of plastic. This is the same material that made up
the magnetic tape. Now, of course, a circle doesn't have any ends so
it is much quicker to find your data - wherever it happens to be on
the disk.
The first magnetic disks were stored in a card sleeve (there's one
shown here in the photo) and it allowed the disk to bend slightly ...
this is why they were called 'floppy' disks. The problem was that this
flexibility often meant that the disks became bent and unusable. "
from:
( http://www.ewart.org.uk/it/hardware/storage/storage.htm )
Further reading:
Very detailed article with in depth details an many detailed pictures:
( http://cma.zdnet.com/book/upgraderepair/ch13/ch13.htm#Heading3 )
Another article in the wikipedia online encyclopedia with many links
and some pictures:
( http://en.wikipedia.org/wiki/Floppy )
On the magnetic data storage format:
( http://en.wikipedia.org/wiki/Disk_storage )
I hope that this helps you to make a good class presentation. If you
need more help or if anything should be unclear please post a request
for clarification.
till-ga
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