can anyone give me a comprehensive description about ORG directive?
When and why is it used in assembly written applications?
Using Nasm on x86 or AMD64.
ORG is used to set the assembler location counter. This may or may not translate to a load address at link time. It can be used to define absolute addresses, e.g. when defining something like interrupt vectors which may need to be at a fixed address, or it can be used to introduce padding or generate a specific alignment for the following code.