Drives and Volumes

A drive letter designates which drive contains the file.  In a file's full 
name, the drive letter is followed by a colon.  Drive letters A: and B: 
are normally reserved for the floppy disk drives. 

Normally, drive C: is the first (or only) hard disk drive.  Most current 
operating systems can divide a large hard disk into multiple logical 
drives or volumes that are usually called C:, D:, E:, etc.  Network 
systems (LANs) give additional drive letters to sections of the network 
file server drives. 

Most recent systems also include a CD-ROM drive.  The CD-ROM is also 
assigned a drive letter (or several letters, for CD-ROM changers), 
typically using letters beyond that used by the last hard disk in the 
system, but before any network drives.  Some systems may have "RAM disks" 
(sometimes called "virtual disks"), which are areas of memory set aside by 
software (a "RAM disk driver") for use as fast but temporary storage. 
 Like CD-ROM drives, RAM disks are usually assigned drive letters beyond 
the last hard disk in the system, but before network drives. 

For example, on a system with a large hard disk you might have A: and B: 
as floppy drives, C:, D:, and E: as parts of the hard disk, F: as a CD-ROM 
drive, G: as a RAM disk, and H: and I: as network drives. 

Each volume is formatted under a particular file system; see File Systems 
for details.  Additional information about disk files and directories is 
available under Directories and Subdirectories, File Names, and File 
Attributes and Time Stamps.