when ever a program is to be compiled the syntax is
necessary and we wont receive the output until a correct
syntax is written 
it shows the errors so debugging becomes easier
the best example is C language

where as in interpreter if we miss any syntax it violates
that particular line and goes to the next line
in this case we may or may not get the required output
it does not show any errors even though its violates the syntax
the best example is HTML

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..

1. Controls the execution of application program.

2. Acts as an interface between the application and the
computer hardware.

Paging avoids the considerable problem of fitting the
varying sized memory chunks onto the backing store, from
which most of the previous memory management schemes suffered.

Paging is transperent to the programmer, eliminates external
fragmentation and thus efficient use of main memory.

Optimal page replacement algorithm.
Bcoz it overcomes the belady's anomaly;
number of page fault is low.