Deep Analysis of Const Qualifier in C

Where does a const variable gets stored exactly and how does it behaviour change? Say for example:

const int i=10; // stores where ?  
main()  
{  
   const int j=20; //stores where?   
   return 0;  
}  

If the answer is Code segment then how does the following code work??

main()  
{  
   const int j=20;  
   int *p;  
   p=&j;  
   (*p)++;   
   return 0 ;  
} 

This code works fine... How it is possible to change a read only memory? How does it really get stored? Please explain it to me in detail.