Amnesia is this post's worst enemy

ROM is another type of memory, as I've mentioned before it is Read Only Memory, which means you cannot edit it and you can only read the already stored information. A CD (Compact Disc) ROM is a very common example of this.

CD ROM
A CD can store up to 700 MB of information in it's own unique form. As you know the computer can only understand the binary system made up of 0's and 1's so we need a way to identify these on the surface of a CD. First of all we need to know what a CD is made of. A CD is made up of 3 layers, the thin paper layer, the metallic layer and the plastic layer. The actual information is stored on the metallic layer, either as a bump or a pit on the surface. A bump or pit tells the difference between a 0 or a 1 and when this information is read by the laser inside the CD Drive, the computer can easily read the information stored on the CD.

Caution: Be careful not to scratch your CD or to use an acidic type marker while writing on the front, this could damage the information stored on the CD. If you do end up with some dents or scratches you can try rubbing across them from the middle outward using toothpaste, try this at your own risk!

Another way to store information is via floppy disk. Floppy disks are not as efficient or as common as CD's but are still perfectly fine to use today.

Lastly if you need to attach an CD Drive or Floppy Drive to your existing computer, you need a cable that will go from the drive to the motherboard.