Thinkpads Forum

x201t comes with Core i5-520UM, Intel spec says:
Clock Speed 1.066 GHz
Max Turbo Frequency 1.866 GHz
Memory Types DDR3-800

x201t also comes with Samsung DDR3-1066 2GBx1 7-7-7-20, CPU-Z shows the memory timings are:
DRAM Frequency 400 MHz
FSB:DRAM 4:12

Above means the DDR3 is working at 800 instead of 1066.

If add another DDR3-1333 4GB 9-9-9-24, it will still work at 800 and can't enhance the performance, right?

welcome to the forum!

800 MHz is the fastest the memory bus will go given intel's specs.   1067 or 1333 modules will simply downclock to 800.

you'd need a standard i5-M processor rather than a UM to get 1067 MHz.