First of all: I hate that you're downvoted when you're explicitly up-front about having zero expertise on this, before putting forward a completely valid hypothesis. Secondly: It's *very* unlikely that formatting is the culprit here. I/O operations (read/write) are *far* slower than CPU operations, especially on spin-discs (like HDD's), they can be several orders of magnitude slower. When you copy data, it's basically - Read data (I/O) - Possibly do some formatting, scanning, whatever (CPU) - Write data (I/O) Whichever of these is your choke-point will determine your speed. It's very unlikely that a pure copy operation will be choked by the CPU-bound task. Much more likely that the read/write speed of the HDD is the culprit.