The Lenovo Thinkpad E520 extended memory is best suited to the \"DDR3 1333Mhz\" specification. The mainboard of the E520 is the Intel HM65 chipset. It is delivered with two memory card slots (a single memory card slot supports a maximum of 4G memory). Memory as long as the same specifications (algebra and frequency) different manufacturers can be compatible, like the general common Kingston, Samsung memory can be used. When the memory is expanded, it is necessary to remove the back shell, unplug the laptop battery and power cord, and it is best to seek help from relevant professionals if you are not familiar with the situation.