Your Toshiba Dynabook SS S21 can support up to 1.25GB of memory. For optimal system performance install the maximum amount of memory in each memory socket, this system comes with standard amount of   256MB 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 Dynabook SS S21.