Dissect a Disk



45 minutes

What do I need?

  • A 3.5-inch computer disk
  • A butter knife
  Mom and kids dissect a disk

What do I do?

1 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.

2 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?

3 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.




  4 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.

5 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.

Parts inside of Disk

  6 Here are all the parts of the disk that you can find if you look carefully:
  • A metal shutter
  • A spring
  • A brown plastic circle from a metal center or hub (The circle is made out of the same stuff cassette tapes and videotapes are made of.)
  • Two white paper rings
  • A small black plastic rectangle with legs (Hint: it's up in one of the corners.)
  • A small plastic flap
  • Two plastic squares that hold everything else
Can you guess why each of these parts is there? How do you think they work together when the disk is inside the computer?

What's going on?

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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This and dozens of other cool activities are included in the Exploratorium's Science Explorer books, available for purchase from our online store .

About the Books

Published by Owl Books,
Henry Holt & Company, New York,
1996 & 1997

ISBN 0-B050-4536 & ISBN 0-8050-4537-6 ,
$12.95 each

© 1998 Exploratorium