Lenovo ThinkPad 770E-ED TP 770X User's Reference that shipped with the system - Page 68

Increasing Memory Increasing Memory Increasing memory capacity is an effective way to make programs run faster. You can increase the amount of memory in your computer by installing a dual inline memory module (DIMM), available as an option. Different capacities of DIMMs are available. You can install a DIMM directly in one of the memory slots on the bottom of the computer. Your computer memory capacity can be expanded up to 320 MB (64-MB base memory and two 128-MB DIMM options). If your computer is equipped with 128-MB base memory, install two 128-MB DIMM options after removing the 64-MB DIMM option that had been installed at the time of purchase. The ThinkPad 770X computer supports the synchronus dynamic random access memory (SDRAM) card only. It does not support the enhanced data output dynamic random access memory (EDO DRAM) card. If you install a DIMM that is not supported by your computer, a 225 error code might appear when the system starts. The appropriate memory option can be purchased through your IBM reseller or IBM marketing representative. 54 IBM ThinkPad 770X User's Reference