There are two main kinds of disks: Magnetic and Optical. Magnetic disks are the old kind and are slowly being replaced. They store data by aligning little pieces of metal inside differently using a magnet. Because of the way they store data magnetic disks can be erased or completely destroyed by magnets, heat, and dust. The two most popular forms of magnetic disks are Hard Disks and Floppy Disks. Hard disks are stored permanently inside their drive, which is normally installed into the computer box where you cannot see any part of it. Hard Disks can store a lot of data, and are used to store most of the information on computers. Floppy disks are small disks that you can pop in and out of their drive. All you can see of their drive is a slit in the computer box with a button and a light. You can put in different disks and then take them out and give them to someone so that you can transfer data between your computers.

Hard disks Hard disks are used to store most of the data on a computer, and can store more than anything else can.

Floppy disks Floppy disks are used to transfer data between computers, but are very small.
   4.4 - a CD

Optical disks are the newer kind of disk. The most popular kind of optical disk is the Compact Disc (CD). CDs can still be put into and taken out of their drive, making them good for buying programs on, and nowadays for transferring data. Normal CDs that you buy with programs on them are CD-ROMs. They are called that because, like ROM, they are read-only. You can also get CD-Rs and CD-RWs, which are not read-only and are not erasable and erasable, respectively. Unlike floppy disks that can store only 1.44 megabytes (MB, that’s 1 048 576 bytes, usually we estimate that it is one million), CDs can store around 700MB! And, because CDs store their information with variations in the shape of the disk that reflects a laser differently they cannot be damaged as easily. However, you should still never touch the shiny surface of the CD. Digital Versatile Discs (DVDs) are another kind of Optical disc that work identically to CDs, however they can store much more information and transfer it at much higher speeds. There is also a new format coming in from Japan that is smaller and faster than DVDs and stores much more information! Today you can also get memory cards that are called flash memory or, more properly, EEPROMs. These are cards that operate just like ROM that isn’t read-only, so they don’t lose their information when the power is cut.

Compact Discs CDs are the most popular form of optical discs.

Digital Versatile Discs Sometimes called Digital Video Discs because of their extensive use in video, DVDs can store more than CDs.