Rom is a storage technology that allows to write the only 
once.After the data has written it can be read for a number 
of times wheras in ram we can  read and write the data any 
num of times.

ROM is a nonvolatile memory whereas RAM is a Volatile memory.

In general terms :

RAM = short term memory , ROM = Long term memory.

In Tecnical terms :

RAM = volatile type , ROM = non volatile type.

Usage:

RAM : used for storing frequently used data,applications
that are currently and frequently running are stored in
RAM.The dat a in RAM lost when power off.

ROM : For permanent storage.Data does't lost when the power
is off.

Reusage :

RAM : Data losts when power off,so easy reusable (volatile).
ROM : Can be reused by erasing or modifying the data by
electronically.

Why RAM instid of ROM :

 Data retrieving method is faster in RAM than ROM.But RAM
costs more.

RAM =RANDOM ACCESS MEMORY..IT IS VOLATILE MEMORY..MEMORY HAS
TO BE LOSE WHILE PC IS TURNED OFF.

ROM =READ ONLY MEMORY..IT IS NON VOLATILE MEMORY..ALL THE
BIOS INFORMATION STORED IN ROM..THIS DATA CANT BE LOSE WHILE
PC IS TURNED OFF..

rom is basically read only memory, and ram random access
memory... what more do you need to no? well a lot more...
bascially this is all you need to no...RAM is short for
Random Access Memory, and comes from hardware components
wired into or attached to the motherboard, the main circuit
board of your computer. RAM is used to run certain basic
programs and functions that your computer needs to operate
correctly, and functions only while the computer is
receiving power. Programs you're using are written in RAM
temporarily while the computer is processing them. Think of
RAM as a playing field, a large open area where your
programs function. Each program takes up a certain amount of
space; the field can accommodate one or several different
programs at one time, but its capacity is limited. When you
shut down a program, it disappears from RAM and (ideally)
the space it occupied can be reused. Sometimes some
operating systems, including Microsoft Windows, won't
relinquish the RAM space even when a program is closed.
However, because stuff in the RAM is retained only while the
computer is powered up, turning it off will always clear the
RAM.
ROM is an acronym for Read Only Memory, a type of
unchangeable memory residing in chips on your motherboard.
ROM contains the bare minimum of instructions needed to
start your computer. Because it's used for critical
functions, it can't be removed short of ripping it out of
the motherboard; adding to it is just as difficult. Think of
it as analogous to municipal utilities, such as gas and
electricity. If you want a different configuration, you'll
have to "move on" to a different motherboard or computer.
Incidentally, the term "ROM" is also used, not entirely
correctly, when referring to some kinds of storage media
that can't be modified, such as CD-ROMs.
Basically, RAM is the size of your playing field, and can be
increased as you purchase more "real estate"; ROM is
equivalent to your utilities, the hardwired bare necessities
needed to operate your computer, and is fixed in size; and
storage capacity can be thought of as warehouses of various
size, some of them mobile, which can be trucked in or
constructed as circumstances warrant.

please don't follow   r.p. jain