slow speeds from SSD on laptop

[babouche]

Hi! I recently installed a ssd on my laptop (asus G751JY). The laptop has 2 slots, first one is occupied by a PCI-E M.2 ssd and the other one is the one which I installed the ssd.Problem is that I only get half the speed(250mb/s read/write) my ssd should have (crucial M500).Anyone knows that's wrong?
Laptop is recent and should support stat 6.0Gps

thanks in advance

 

[Oddba11]

It's possible the slots are not identical. How are you measuring the speed?