Your HewlettPackard Compaq ProBook 6555b can support up to 8GB of memory. For optimal system performance install the maximum amount of memory in each memory socket, this system comes with standard amount of   2GB or 4GB (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 HewlettPackard Compaq ProBook 6555b.