File compare utility

I need an Explorer type utility that compares the content of two folders. I back up my files from my computer to an external drive and maintaining this back up manually is a real pain. What I do not want is a program that bundles all the files on my computer into a monster file in an obscure format. I want to be able to take my external drive anywhere and have exactly the same folder structure with all the same files right off the bat. Frankly this is so basic that I do not understand why Windows does not have this as standard. Or am I missing something? ## Deliverables I need is a screen showing side by side the two locations and highlighting the differences in content: - any file or folder present with the same name on one and missing on the other - any file or folder present on both with the same name but with different dates By location I mean any place in my Windows Explorer, i.e. the two locations could be on separate physical drives (both external, one external, or both internal), anywhere in the folder structure. I need to be able to choose which way to resolve each discrepancy ('synchronise'), i.e. whether to update from A to B or B to A. And I need the screen to update in real time so the list of discrepancies shrinks as I hit the arrows. I am not sure about the exact layout of the screen, this should be discussed with the developer. The utility should be a single executable and look and work like the Windows Explorer. ## Platform Windows XP Home/Pro and Vista