Your IBM PS/1 386SX Model 2121 can support up to 6 MB of memory. For optimal system performance install the maximum amount of memory in each memory socket, this system comes with standard amount of   2 MB (non-removable) 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 IBM PS/1 386SX Model 2121.