if you have 2 operating system on one HDD, mean linux and
windows now, if u wants to use the D:\ of windows then u can
use mount command.

after mounting D:\ u can directly put u r data from linux 

when u re-boot system and login to windows then u will be
able to use that data.

mount is a command which is used to copy or to use the 
files or folders which are in windows into ur linux.

coomand:
mount /dev/hda5 /mnt/temp

The process of adding or linking or mapping the formatted
disk space to a folder is called mounting.
Like the boot partition is formatted in ext2/3 filesystem
and then it is mounted to /boot folder.You cannot use any
partition or disk without mounting

mount is used for mounting the devices and filesystem it is
a command utility for mounting devices

mount is nothing but a command which displays the already 
mounted file systems.

In computers, to mount is to make a group of files in a 
file system structure accessible to a user or user group. 
In some usages, it means to make a device physically 
accessible.

In a UNIX environment, the mount command attaches discs, or 
directories logically rather than physically. The Unix 
mount command makes a directory accessible by attaching a 
root directory of one file system to another directory, 
which makes all the file systems usable as if they were 
subdirectories of the file system they are attached to.

Unix recognizes devices by their location, as compared to 
Windows, which recognizes them by their names (C: drive, 
for example).


Command Usage example:
$ mount	/dev/hda1	/mnt/temp