Users at the NotebookReview Forum have discovered that solid state disks perform poorer than they should on laptops with the Intel PM55 and HM55 chipsets.
After lots of investigation, it appears that a software-based power management feature is likely to blame for the problem. Many users confirmed that the performance hit disappears when Windows is booted into safe mode or when the processor is fully loaded via a CPU stress tool, and the issue is also resolved when the C-states are deactivated in the BIOS, but this option is not available on all laptops.
On the screenshot below you can see the CrystalDiskMark results of a user who ran a couple of tests on his Intel X18M G2 160GB SSD. As you can see the 4K read/write performance receives a pretty big hit, in safe mode the disk delivers a read speed of 22.43MB/s and a write speed of 62.20MB/s, while during regular operation the SSD delivers only 15.05MB/s and 23.49MB/s in the benchmark.
Several people have reported the issue to Intel and laptop makers, hopefully a fix will be made available soon.