Dear suraj, 

As per your query there is sure difference between core and software companies. Core companies mainly hire engineers of mechanical, civil, electrical department which mainly has to do with things like VSIL, microprocessor and other core stuff. Whereas in a software company engineers from computer and information technology department are hired. For working is a software company you need to be updated about the latest software and technical trends whereas you need to be really hardworking to work in a core company which is also slightly applicable for software companies. Hope this helps!