Copying Hard Drives

I’m embarrassed to say, but I haven’t copied a hard drive since school, and have forgotten the proceedures. I have a new 20Gig drive I want to copy to from a 15 Gig. The 20 is 7200 rpm Vs. 5600 for the 15. I recall a command xcopy32, but that is all. (dummy). Can I copy from slave to master, or does it have to be in reverse. All help will be appreciated. Thanks in advance. Chuck