5400 and 7200 hd

You may see some speed improvement, depending what it is used for. You will only see faster DVD burns if the old drive was the limiting factor.

The rotational speed won't make that much difference, it has only increased by 33%. One rotation takes 0.139ms instead of 0.185ms, hardly a big difference. But the seek time has improved dramatically. Before it was probably about 10ms average, now it is probably down to 8.5ms. That doesn't sound a lot at first, but it means that the old max seek time was 20ms to cover 15GB, the equivalent of 1.33GB/ms. It is now 17ms to cover 120GB, equivalent to 7.05GB/ms which is over 5 times as fast.

Thanks for the great explanation Lynx....It does seem a little quicker and it is really nice to have the extra space ...