Your Toshiba C855-S5111 can support up to 16 GB of memory. For optimal system performance install the maximum amount of memory in each memory socket, this system comes with standard amount of   4 GB RAM. One or more of the sockets in the system might be already filled with memory. Whenever you upgrade, you can either add memory to one of the open sockets and/or remove memory from a filled socket and replace it with a higher capacity memory module. Select your Memory Upgrade for Toshiba C855-S5111.