We recently upgraded the memory on our Lenovo X220 to be better able to run 64-bit Windows 10.
The machine originally came with Elpida EBJ21UE8BFU0-DJ-F DDR3-1333 2048MB memory. This memory has 8 chips on each side of the SO-DIMM,
The upgrade memory is Elpida EBJ40UG8EFU0-GN-F DDR3L-1600 4096MB. This memory has 4 chips on each side of the SO-DIMM. DDR3L is low power memory which can operate at 1.35V if the machine supports it. DDR3L is able to run at the JEDEC standard 1.5V easily. The Lenovo X220 supports 1.35V operation with DDR3-L memory which can slightly improve the power load.
Elpida is owned by Micron who is one of the remaining manufacturers of PC memory.
The machine is capable of using 8192MB sticks but prices are rather high.
The modified BIOS is also able to run the memory at DDR3-1600 speeds. This alone makes the machine feel a bit faster due to the higher memory bandwidth. We noted that Lenovo actually throttled memory speeds with more recent BIOS updates which is hard to understand.
The HD 3000 has to use system memory so having additional memory seems to benefit this as well. The HD 3000 is on die so it shares L2 cache with the CPU cores and main memory acts for both the CPU and GPU.
Installing the memory is easy with 2 screws to open the cover and pop out to old sticks. The new memory pops in easily and the machine can boot from cold start to ready in 30 seconds.