Difference between .lib file and .obj file

The .lib file is a file that has the stuff the linker needs to build your executable program. Windows cannot use them, but compilers and linkers can. Its a lot like a .obj file really, except it contains everything needed for all the stuff in your 'library' whereas an obj is from a single source file. It also contains a protocol for the associated .dll (basicaly, offsets of where functions start, the name and parameters(?) of the functions, calling conventions(?) and things like this).

A .dll can have a lot of different stuff -- data, functions, anything really. A dll that has shared routines is what the OS needs to run those routines -- compare this to a 'mini executable'. A program smoothly jumps from its own executable statements to the ones in the .dll and back again. Windows does some smoke and mirrors here to make the file loading efficient(ish).

@sherya
can you elaborate it please "It also contains a protocol for the associated .dll".
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what the protocol means in that envoirnment.