Might be something else going on with the computer, but if you expect any kind of useful advice it might help by posting the entire specs of your system, but no Transferring files from folder to folder or to another drive barely engages the CPU, if at all.
Now if you're talking about archiving files with winrar, or winzip or something like that, yes that is a CPU workload. And if the speeds are bad, there is something going on.
See here. I'm running this transfer now between my 2 hard drives, my CPU usage hasn't gone above 15 percent in the last 5 minutes.