I want to use a USB external hard drive for backup. However, I like backing up with XCOPY because I can easily write a script to quickly copy only those files that have changed. But the problem is, plugging in a USB drive cannot guarantee the drive letter, right? Wouldn't it assign whatever drive letter it feels like at the time of plug in? Is it somehow possible to force it to always assign a particular drive letter?

I know many external drives come with software that can do this kind of backup - only backing up the files that have changed. However, I didn't want to buy an external drive. I was planning to save money by buying only an external enclosure and using one of my old drives. Thus, I won't get any software.