The hard drive is your main form of data storage in your computer. It is where you store your computer's operating system and other software you use. When picking a hard drive, you will want to make sure how much memory you need depending on what you use your computer for and data transfer speeds as well.
A drive in your computer that allows you access/write data to compact disks. When you are looking for a cd drive, you will want to look for features such as if the drive can write to a cd, and its write speed.
A drive that allows you to read and/or write to Digital Versatile Discs. Just like CD drives, you will want to see if the just reads the discs or can read/and write.
The newest type of disc drives that offer increased data storage over DVDs. Of course they are the most expensive available now. Make sure to look for the same characteristics you would when shopping for the othe types of disc drives.