This is a virtual folder which displays
all volumes on the computer. A volume is a single storage location, usually with a single, drive letter unique to the computer. It can be an entire hard (or floppy) drive, a partition within a drive, a removable (eg. USB) drive, an optical drive (ie. CD, DVD or Blu-Ray Disc™, or a “drive” (with a drive letter) assigned to a folder in the NTFS file system.
virtual folders, such as Control Panel
renamed real locations such as Bob’s Documents (probably C:\Documents and Settings\Bob\My Documents) and Shared Documents (probably C:\Documents and Settings\All Users\Documents); drive letters may vary with different installations of Windows.
Note that My Computer may contain different items, or may display differently in each version of Windows.