i had just recently bought a Samsung 840 evo 250gb SSD,
and after installing the windows on it,
my old HDD became very very slow when reading,
and the computer boot time took longer than before when just using the HDD.
my SSD is working fine,
reading and writing with excellent speed.
And if unplugged the HDD,
the boot time will also run fast as it's supposed to be as a SSD.