This question already has an answer here:
My boss was saying it takes longer to copy two files at the same time than doing one and then the other because the hard drive has to keep switching the head between the two locations on disk. Is this true? It seems to me that the operating system should be smart enough to fix this (i.e., it should know to copy them sequentially). Is this true when copying to a drive connected to a USB port?
EDIT: are there any other factors regarding the files system that factors in? For example does it make a difference copying 1 directory containing 10 files versus copying 10 files from all over the disk? I'm wondering only about one source medium and one destination medium (no reading from multiple drives).