Why Cache Is Needed? Explain

First of all cache memory is very fast memory that the processor can
access much
more quickly than main memory or RAM.  Currently processors can operate at
speeds
much greater than affordable, reliable memory can supply the necessary data.
Cache
memory, is much like other memory, except it can operate much faster, and
much more
expensive.

Cache memory attempts to bridge the gap between fast, expensive memory that
can
be made in limited quantities, and the large amounts of RAM needed for
modern
applications.  By giving the processor a small amount of fast memory to
used, and then
having that memory read in and write to main memory in "spare" time, the
processor can
operate at full speed much of the time.