What is the Difference between ANSI C and non-ANSI C ?

Hi !!,
I wanted to know as to what is the difference between ANSI C and non-ANSI C ? This surely has to do something with the type of compilers used but then whats the precise difference ?
Is the C compiler provided with Linux ANSI compliant ? I would be extremely thankful if anyone could tell me the difference.

There were a lot of compilers uncompatible with each other before a standardization was set by ANSI in 1988. For example the following code may work on some compilers and won't in others.

printf("st" "sd" "45");

The compatible one was
printf("st" , "sd" , "45");

So ANSI set standards for some basic libaries, basic keywords, language rules. Today nearly all of the compilers you will find are ANSI C compliants. This means that they all support the ANSI rules. However they may add new features which are not present in ANSI C.

The C compiler in Linux, gcc, is also ANSI C compliant. But some improvements are made for better code generation.
Write
man gcc
and see how these are arranged by various flags.