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What's inside a computer disk?
When you take apart a 3.5-inch disk, you'll end
up with two colored plastic squares (the housing) that hold the other, smaller
parts. Here's a guide to what each of those parts is, and what it does when
the disk is inside your computer.
· Shutter
This is a
piece of metal folded over one edge of the disk. That edge goes into the
computer first. Inside the computer, the shutter slides over, and the information
on the disk can be read through the rectangular slot.
· Spring
When the disk
comes out of the machine, the spring snaps the shutter closed again so no
dust or fingerprints can get onto the magnetic disk.
· Magnetic disk
This
round piece of plastic is coated with iron oxide. Iron oxide can be magnetized.
When you save information to a disk, a recording head creates a magnetic
pattern on the iron oxide. The pattern stores your words or pictures in
a form that the computer can read the next time you put the disk in.
· Hub
The metal center
of the magnetic disk. The holes in the hub are like the hole in the middle
of a record-they fit over spindles inside the computer and hold the disk
in place while it spins.
· Paper rings
The magnetic
disk is sandwiched between two white paper rings. The two rings are glued
down to the plastic housing, and stay still while the disk spins. They clean
the disk, removing microscopic bits of dust.
· Write-protect tab
This little plastic rectangle is in the upper right corner of most disks.
It slides up to reveal a square hole in the housing (or slides down, to
cover the hole). When the hole is open, the disk is locked. Your computer
won't allow you to add anything to the disk or erase anything from it.
· Plastic flap
You have
to hunt for this piece. It's tucked away under one of the paper rings. One
end is glued down, and the plastic is bent, just a little. It functions
as a simple spring that pushes the paper ring tight against the surface
of the magnetic disk.
What's inside a cassette tape?
Now that you've taken apart a floppy disk, you
may want to try dissecting an audiocassette or a video-cassette. A lot of
the parts on these cassettes are very similar to parts of a floppy disk.
How many can you find?
· Magnetic tape.
· Hubs. There are two plastic wheels in the middle
of a cassette. The tape winds from one to the other as they spin inside
the machine.
· Write-protect tab. You can punch it out so no
one can re-record over your favorite song or TV show.
· A piece of paper or felt (and a simple spring)
that cleans the tape while it's moving.
· A shutter (and a spring) to keep dirt and fingers
from getting to the tape. (Only on a videocassette.)
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Ask a grown-up for a computer disk that you can
take apart. DON'T just take one! It might have important stuff on it.
Pretend you've never seen a disk before, and look
at the outside of it carefully. What different parts can you find? Do any
of them move? Does anything change when you move those parts?
Now look for the places where the disk will come
apart. You can take it apart any way you want, but an easy way to start
is to use a butter knife to carefully pry up the metal rectangle-the shutter-that
folds over one edge of the disk. Pull it off and put it aside.
Now you can see some slots in
the plastic. Put the knife in a slot and gently pry apart the two flat halves
of the disk. Don't just snap the disk apart, or you'll lose the tiny spring
inside. It held the shutter closed and may jump out, so watch for it. The
plastic at the corners of the disk will probably crack or break off. That's
okay.
Do the two halves of the disk look the same? What
parts can you see? You may want to draw a picture of where everything is
before you take the disk apart any further.
Here are all the parts of the
disk that you can find if you look carefully:
