The Macintosh Operating System utilizes a Graphical User Interface (GUI) for user interaction, and thus has a desktop. In fact, the Macintosh OS was the first successful OS to implement a GUI. The desktop gives the user easy access to both programs and system tools, and at the same time it manages all of these programs in a way that optimizes user productivity. Below is a picture of a Macintosh OS X desktop, of which the key features are explained further below.
While any icon can be placed on the desktop, drive icons always appear there. Below are some common drive icons you may see on the desktop. Note: it is possible to change any icon on your computer.
This icon is used to represent most hard drives that are attached to your computer. It is the most basic drive icon, there are others depending on the type of hard drive that you have attached (FireWire, USB, etc.). Most computers will boot from one of these devices, since it is the best place to keep a System Folder (the place where all of the Macintosh OS system files are kept) because they have the best combination the largest capacities and the fastest data transfer rates.
This icon represents any floppy or Zip disk, or any other type of portable media that you may be able to attach to your computer. Also, whenever "mounting" a disk image (a file that is an exact representation for a disk) this is the default icon. The disk image resides in temporary memory, and if you log out it will disappear from your desktop.
This icon is used to represent an optical storage disk such as a CD-ROM, DVD, CD-RW, or CD-R. Optical Storage has become a great medium for transporting a large amount of data quickly across machines and platform. Many optical storage mediums will override this icon with one of their own, thus very few discs that you insert will have this icon. Note: It is even possible to add your own icon when burning a CD.
This icon represents any Network volume that you have mounted on your desktop. To connect to the network simply make sure that you have the finder in the foreground and then go to Go -> Connect to Server... You will usually be asked to provide a User Name and Password, but it is not uncommon for you not to be. Once you have selected the volume to mount this icon will appear on your desktop along with the name of the volume of which you chose. This is a temporary item on your desktop, and will disappear if you log out of your computer.
Any drive that appears on your desktop is said to be "mounted," and can be "unmounted." For the most part you can think of unmounting and ejecting as the same thing. To unmount a drive simply drag the icon to the trash icon in the dock. You will notice that the trash icon changes to an eject icon as you drag the drive toward the trash. There is one exception to this rule for ejecting, that is when you wish to eject writable optical media (such as CD-Rs, CD-RWs and DVD-Rs). To eject without burning writable media, click and hold the mouse button on the media you wish to eject, then select eject from the menu that appears.