title: How do patches and service packs work?
body: <p>How do patches or service packs work? I don't know how to explain my question but I will give a try</p>
  
  <p>Take Windows for example. It has files which altogether consume 100s of MB. Now a single service pack (may be 300 MB file) updates the whole windows OS.</p>
  
  <p>Similarly I have seen updates happening for softwares like adobe reader etc. In all these cases the main exe is much larger compared to the update. How does the process work? If the main file refers any dependancy files and if the update change the version or size. Will it not affect the exe? </p>