240 heads on your harddrive is from an older addressing system - in comparison to a 255 heads addressing system, the maximum capacity of the hard drive is limited. Could it be because your original drive is a small-capacity older drive or an upgrade from XP?
The 240 heads is a binary reference the actual number of physical heads you have on your hard drive. With SSDs there are no heads, so that is just a reference point.
Anyway, point is, it should not make much of a difference. In fact, I suggest you try to force them to match as 255 is the newer by far more common standards now. It might cause some errors though, and if your drive is working as it is, with the full capacity allocated, and if you run some speed tests and it matches, leave it as it is.