Permanent storage in a computer can take one of two forms, internal or removable. The hard drive is considered internal storage. Removable storage includes things like floppy disks, backup tapes, USB drives, and CDs. Using the recording protection tabs can protect media (disks) from being deleted or written on accidentally, just the same as on VHS and cassette tapes. Unlike RAM, which stores data using electricity, permanent storage devices and media store data electromagnetically, so the data remains when the power goes off.
ROM is another type of permanent storage. It stands for Read Only Memory and can never be rewritten. All modern computers include ROM that contain start-up information and other critical information. The only way to change ROM is to replace the ROM chip. Most users never have to do something like this. CDs are sometimes referred to as a CD-ROMs, because you can only read it, not write to it.
There are and have been many different types of disks for many different uses. The first disks that were used were 8" floppy disks, which soon shrunk to the more commonly known 5¼" floppy disks. Later, the 3½" disk was invented. This disk is stored in a hard, plastic case. Many novice students called it a hard disk because it was enclosed in a hard case; however, the disk inside is still a floppy disk.
Improper handling can damage floppy disks. Never bend them, expose them to heat or cold, touch the read/write slot, place heavy objects on them, or remove them from the drive while the drive is reading them. Floppies are very prone to failure because they are not made of high quality material. Most errors come from being ejected while the drive is still writing to the disk, but they often have physical failures as well.
Backup tapes can often hold large quantities of data, but require special hardware that is not installed on most computers. Although they can hold large amounts of data, accessing that data can be very slow, since the drive has to fast forward through the tape to find the data it needs. They are normally used for backing up servers with large amounts of data, not personal PCs.
Hard disks are similar to floppy disks, but are made out of metal and usually are rarely removed by the user. Most of the time hard disks are actually several disks stacked on top of each other contained in a case. This case is called a hard drive and is installed inside the computer. Information can be saved to and retrieved from a hard disk much faster than on a floppy disk so they are used to store large files and programs. The main hard drive on most computers is usually referenced as the C: drive. It is not entirely uncommon to find personal computers with multiple hard drives. Servers almost always have multiple hard drives. Data can often be recovered off a hard drive if it is deleted or if the hardware is damaged because of the way the data is stored, but you'll probably need to contact a professional with special tools. They can be damaged by power surges, magnets, vibration, and heat.
A standard 3.5-inch
floppy disk can hold up to 1.44 MB of data, which really isn't very much. An average size hard
drive can hold 40-140 GB. Some hard drives will hold several hundred GB.
USB drives (thumbdrives, memory sticks) can be attached to a key chain or clipped to a shirt pocket. The storage capacity on these disks varies. Popular sizes range from 512 MB to 2 GB, although they go higher than that. They are much more durable and easy to use than floppies, wich is why they have become so popular, but they are also prone to errors if you pull the drive out while the computer is writing to it.
Another way of storing data is on a CD or DVD. A CD can hold 700 MB, and a DVD can hold 4.7 GB or more. A special drive is needed to read these discs and write to them. A drive that can write to a CD or DVD is often called a burner because the data is burned into the disc with a laser. A laser is also used to read the data on the disc.
The following are various types of discs that can be used:
CD-R - CD recordable, disc can be
recorded one time.
CD-RW - CD rewritable, disc can be written and over-written repeatedly.
DVDs - There are also different formats of recordable DVD discs. DVD-R and DVD+R are the most common, but there are several other types. They can only be used in drives that support that format, but most new drives support both. Just make sure when you buy DVDs for your burner that they are compatible, especially if your DVD drive is more than a couple years old. A CD drive won't read a DVD, but DVD drives will read CDs.